/*****************************************************************************
*
* MODULE:       DBF driver 
*   	    	
* AUTHOR(S):    Radim Blazek
*
* PURPOSE:      Simple driver for reading and writing dbf files     
*
* COPYRIGHT:    (C) 2000 by the GRASS Development Team
*
*               This program is free software under the GNU General Public
*   	    	License (>=v2). Read the file COPYING that comes with GRASS
*   	    	for details.
*
* DBF API:      http://shapelib.maptools.org/dbf_api.html
*****************************************************************************/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <dbmi.h>
#include <shapefil.h>
#include "globals.h"
#include "proto.h"

/* Results of eval_node */
#define NODE_FALSE  0
#define NODE_TRUE   1
#define NODE_VALUE  2
#define NODE_NULL   3
#define NODE_ERROR  4

int yyparse(void);
void get_col_def ( SQLPSTMT *st, int col, int *type, int *width, int *decimals );
int sel(SQLPSTMT * st, int tab, int **set);
int set_val(int tab, int row, int col, SQLPVALUE * val);
double eval_node(SQLPNODE *, int, int, SQLPVALUE *);
int eval_node_type(SQLPNODE *, int);

int execute(char *sql, cursor * c)
{
    int i, j, tab, ret;
    SQLPSTMT *st;
    ROW *dbrows;
    VALUE *dbval;
    int row, nrows;
    int *cols, ncols, col;
    int *selset;
    int dtype, stype;
    int width, decimals;
    char *tmpsql, name[500];

    /* parse sql statement */
    /* I don't know why, but if the statement ends by string in quotes 'xxx' and is not 
    *  followed by space or '\n' it is not parsed properly -> */
    tmpsql = (char*) G_malloc ( strlen(sql) + 2 );
    sprintf ( tmpsql, "%s ", sql );
    st = sqpInitStmt();
    st->stmt = tmpsql;
    sqpInitParser(st);

    if (yyparse() != 0) {
	sqpFreeStmt(st);
	free ( tmpsql) ;
	append_error("SQL parser error in statement:\n%s\n", sql);
	return DB_FAILED;
    }
    free ( tmpsql) ;

    G_debug (3, "SQL statement parsed successfully" );

    /* sqpPrintStmt(st); */ /* debug output only */

    /* find table */
    tab = find_table(st->table);
    if (tab < 0 && st->command != SQLP_CREATE) {
	append_error("Table '%s' doesn't exist.\n", st->table);
	return DB_FAILED;
    }

    /* For DROP we have to call load_table_head() because it reads permissions */
    if ((st->command != SQLP_CREATE)) {
	ret = load_table_head(tab);
	if ( ret == DB_FAILED ) { 
	    append_error( "Cannot load table head.\n");
	    return DB_FAILED;
	}
    }

    if ((st->command == SQLP_DROP) || (st->command == SQLP_DELETE) ||
        (st->command == SQLP_INSERT) || (st->command == SQLP_UPDATE) || (st->command == SQLP_ADD_COLUMN)
    ) {
	if ( db.tables[tab].write == FALSE ) {
  	    append_error( "Cannot modify table, don't have write permission for DBF file.\n");
	    return DB_FAILED;
	}
    }
    
    /* find columns */
    ncols = st->nCol;
    if (st->command == SQLP_INSERT || st->command == SQLP_SELECT
	|| st->command == SQLP_UPDATE) {
	if (ncols > 0) {	/* colums were specified */
	    cols = (int *) malloc(ncols * sizeof(int));
	    for (i = 0; i < ncols; i++) {
		cols[i] = find_column(tab, st->Col[i].s);
		if ( cols[i] == -1 ) {
	            append_error( "Column '%s' not found\n", st->Col[i].s);
	            return DB_FAILED;
		}
	    }
	}
	else {			/* all columns */

	    ncols = db.tables[tab].ncols;
	    cols = (int *) malloc(ncols * sizeof(int));
	    for (i = 0; i < ncols; i++)
		cols[i] = i;
	}
    }

    /* check column types */
    if (st->command == SQLP_INSERT || st->command == SQLP_UPDATE) {
	for (i = 0; i < st->nVal; i++) {
	    col = cols[i];
	    if ( st->Val[i].type != SQLP_NULL ) {
		dtype = db.tables[tab].cols[col].type;
		stype = st->Val[i].type;
		if ((dtype == DBF_INT && stype != SQLP_I)
		    || (dtype == DBF_DOUBLE && stype == SQLP_S)
		    || (dtype == DBF_CHAR && stype != SQLP_S)) {
		     append_error("Incompatible value type.\n");
		    return DB_FAILED;
		}
	    }
	}
    }

    /* do command */
    switch (st->command) {
    case (SQLP_ADD_COLUMN):
	load_table(tab);
	get_col_def ( st, 0, &dtype, &width, &decimals );
	ret = add_column(tab, dtype, st->Col[0].s, width, decimals);
	if ( ret == DB_FAILED ) {
	    append_error("Cannot add column.\n");
	    return DB_FAILED;
	}
	/* Add column to each row */
	for ( i = 0; i < db.tables[tab].nrows; i++ ) {
	    db.tables[tab].rows[i].values = 
	        (VALUE *) realloc( db.tables[tab].rows[i].values, db.tables[tab].ncols * sizeof(VALUE));

            dbval = &(db.tables[tab].rows[i].values[db.tables[tab].ncols-1]);
	    dbval->i = 0;
	    dbval->d = 0.0;
	    dbval->c = NULL;
	    dbval->is_null = 1;
	}
	db.tables[tab].updated = TRUE;
	break;

    case (SQLP_CREATE):
	if (tab >= 0) {
	    append_error("Table %s already exists\n", st->table);
	    return DB_FAILED;
	}
	sprintf ( name, "%s.dbf", st->table );
	add_table(st->table, name );
	
	tab = find_table(st->table);
	db.tables[tab].read = TRUE;
	db.tables[tab].write = TRUE;

	for (i = 0; i < ncols; i++) {
	    get_col_def ( st, i, &dtype, &width, &decimals );
	    ret = add_column(tab, dtype, st->Col[i].s, width, decimals);
	    if ( ret == DB_FAILED ) {
		append_error("Cannot create table.\n");
	        db.tables[tab].alive = FALSE;
		return DB_FAILED;
	    }
	}
	db.tables[tab].described = TRUE;
	db.tables[tab].loaded = TRUE;
	db.tables[tab].updated = TRUE;
	break;

    case (SQLP_DROP):
	unlink(db.tables[tab].file);
	db.tables[tab].alive = FALSE;
	break;

    case (SQLP_INSERT):
	load_table(tab);

	/* add row */
	if (db.tables[tab].nrows == db.tables[tab].arows) {
	    db.tables[tab].arows += 1000;
	    db.tables[tab].rows =
		(ROW *) realloc(db.tables[tab].rows,
				db.tables[tab].arows * sizeof(ROW));
	}
	dbrows = db.tables[tab].rows;
	row = db.tables[tab].nrows;
	dbrows[row].values =
	    (VALUE *) calloc(db.tables[tab].ncols, sizeof(VALUE));
	dbrows[row].alive = TRUE;
        
	/* set to null */
	for (i = 0; i < db.tables[tab].ncols; i++) {
      	    VALUE *dbval;

            dbval = &(dbrows[row].values[i]);
	    dbval->is_null = 1;
	}

	/* set values */
	for (i = 0; i < st->nVal; i++) {
	    col = cols[i];
	    set_val(tab, row, col, &(st->Val[i]));
	}

	db.tables[tab].nrows++;
	db.tables[tab].updated = TRUE;
	break;

    case (SQLP_SELECT):
	G_debug ( 2, "SELECT");
	c->st = st;
	c->table = tab;
	c->cols = cols;
	c->ncols = ncols;
	c->nrows = sel(st, tab, &(c->set));
	if (c->nrows < 0) {
	    append_error("Error in selecting rows\n");
	    return DB_FAILED;
	}
	c->cur = -1;

	break;

    case (SQLP_UPDATE):
	nrows = sel(st, tab, &selset);
	if (nrows < 0) {
	    append_error("Error in selecting rows\n");
	    return DB_FAILED;
	}
	dbrows = db.tables[tab].rows;

	/* update rows */
	for (i = 0; i < nrows; i++) {
	    row = selset[i];
	    for (j = 0; j < st->nVal; j++) {
		col = cols[j];
		set_val(tab, row, col, &(st->Val[j]));
		db.tables[tab].updated = TRUE;
	    }
	}
	break;

    case (SQLP_DELETE):
	nrows = sel(st, tab, &selset);
	if (nrows < 0) {
	    append_error("Error in selecting rows\n");
	    return DB_FAILED;
	}
	dbrows = db.tables[tab].rows;

	/* delete rows */
	for (i = 0; i < nrows; i++) {
	    row = selset[i];
	    dbrows[row].alive = FALSE;
	    db.tables[tab].updated = TRUE;
	}
	break;

    }
    if ( st->command != SQLP_SELECT ) { /* because statement is released with cursor */
        sqpFreeStmt(st);
    }

    return DB_OK;
}

/* for given parser result and column index finds dbf column definition */
void get_col_def ( SQLPSTMT *st, int col, int *type, int *width, int *decimals )
{
    switch (st->ColType[col]) {
	case (SQLP_INTEGER):
	    *type = DBF_INT;
	    *width = 11;
	    *decimals = 0;
	    break;
	case (SQLP_VARCHAR):
	    *type = DBF_CHAR;
	    *width = st->ColWidth[col];
	    *decimals = 0;
	    break;
	case (SQLP_DATE):  /* DATE treated as string unless SHAPELIB/DBFLIB supports date type */
	    *type = DBF_CHAR;
	    *width = 10;   /* 2004-01-23 = 10 chars */
	    *decimals = 0;
	    break;
	case (SQLP_DOUBLE):
	    *type = DBF_DOUBLE;
	    *width = 20;
	    *decimals = 6;
	    break;
    }
}

int set_val(int tab, int row, int col, SQLPVALUE * val)
{
    VALUE *dbval;

    dbval = &(db.tables[tab].rows[row].values[col]);
	

    if ( val->type == SQLP_NULL ) {
        dbval->is_null = 1;
	dbval->c = NULL;
	dbval->i = 0;
	dbval->d = 0.0;
    } else { 
        dbval->is_null = 0;
	switch (db.tables[tab].cols[col].type) {
	    case DBF_INT:
		dbval->i = val->i;
		break;
	    case DBF_CHAR:
		save_string(dbval, val->s);
		break;
	    case DBF_DOUBLE:
		if (val->type == SQLP_I)
		    dbval->d = val->i;
		else if (val->type == SQLP_D)
		    dbval->d = val->d;
		break;
	}
    }
    return (1);
}

/* Comparison of 2 rows */
static int cur_cmp_table;
static int cur_cmp_ocol;
static int cmp_row ( const void *pa, const void *pb ) 
{
    int *row1 = (int*) pa;
    int *row2 = (int*) pb;
    char *c1, *c2;
    int i1, i2;
    double d1, d2;
    TABLE *tbl;

    tbl = &(db.tables[cur_cmp_table]);
    
    switch ( tbl->cols[cur_cmp_ocol].type ) {
	case DBF_CHAR:
	    c1 = tbl->rows[*row1].values[cur_cmp_ocol].c;
	    c2 = tbl->rows[*row2].values[cur_cmp_ocol].c;
	    return ( strcmp(c1, c2) );
	    break;
	case DBF_INT: 
	    i1 = tbl->rows[*row1].values[cur_cmp_ocol].i;
	    i2 = tbl->rows[*row2].values[cur_cmp_ocol].i;
	    if ( i1 < i2 ) return -1; 
	    if ( i1 > i2 ) return 1; 
	    return 0;
	    break;
	case DBF_DOUBLE: 
	    d1 = tbl->rows[*row1].values[cur_cmp_ocol].d;
	    d2 = tbl->rows[*row2].values[cur_cmp_ocol].d;
	    if ( d1 < d2 ) return -1; 
	    if ( d1 > d2 ) return 1; 
	    return 0;
	    break;
    }
    return 0;
}

/* Select records, sets 'selset' to new array of items and returns
*  number of items or -1 for error */
int sel(SQLPSTMT * st, int tab, int **selset)
{
    int i, ret, condition;
    int *set;			/* pointer to array of indexes to rows */
    int aset, nset;

    G_debug ( 2, "sel(): tab = %d", tab);

    *selset = NULL;
    nset = 0;

    ret = load_table(tab);
    if ( ret == DB_FAILED ) {
	append_error( "Cannot load table.\n");
	return -1;
    }

    aset = 1;
    set = (int *) malloc(aset * sizeof(int));

    if (st->upperNodeptr) {
	int node_type;
	/* First eval node type */
	node_type = eval_node_type( st->upperNodeptr, tab);
	G_debug(4, "node result type = %d", node_type);
	
	if ( node_type == -1 ) {
	    append_error( "Incompatible types in WHERE condition.\n");
	    return -1;
	} else if ( node_type == SQLP_S || node_type == SQLP_I || node_type == SQLP_D ) {
	    append_error( "Result of WHERE condition is not of type BOOL.\n");
	    return -1;
	} else if ( node_type == SQLP_NULL ) { 
	    /* Conditions has undefined result -> nothing selected */
	    return 0;
	} else if ( node_type == SQLP_BOOL ) {  
	    for (i = 0; i < db.tables[tab].nrows; i++) {
		SQLPVALUE value;

		G_debug(4, "row %d", i);
		condition = eval_node( st->upperNodeptr, tab, i, &value);
		G_debug(4, "condition = %d", condition);

		if ( condition == NODE_ERROR ) { /* e.g. division by 0 */
	    	    append_error( "Error in evaluation of WHERE condition.\n");
		    return (-1);
		} else if ( condition == NODE_TRUE ) { /* true */
		    if (nset == aset) {
			aset += 1000;
			set = (int *) realloc(set, aset * sizeof(int));
		    }
		    set[nset] = i;
		    nset++;
		} else if ( condition != NODE_FALSE && condition != NODE_NULL ) { /* Should not happen */
		   append_error( "Unknown result (%d) of WHERE evaluation.\n", condition); 
		   return -1;
		}
	    }
	} else { /* Should not happen */
	    append_error( "Unknown WHERE condition type (bug in DBF driver).\n");
	    return -1;
	}
    } else { /* Select all */
	aset = db.tables[tab].nrows;
	set = (int *) realloc(set, aset * sizeof(int));
	for (i = 0; i < db.tables[tab].nrows; i++) {
	    set[i] = i;
	}
	nset = db.tables[tab].nrows;
    }

    /* Order */
    if ( st->command == SQLP_SELECT && st->orderCol ) {
	G_debug(3, "Order selection by %s", st->orderCol);
    
        /* Find order col */
	cur_cmp_ocol = -1;
	for ( i = 0; i < db.tables[tab].ncols; i++ ) {
	    if ( strcmp ( db.tables[tab].cols[i].name, st->orderCol ) == 0 ) {
		cur_cmp_ocol = i;
		break;
	    }
	}
	if ( cur_cmp_ocol < 0 ) {
	    append_error( "Cannot find order column '%s'\n", st->orderCol);
	    return -1;
	}

	cur_cmp_table = tab;
	qsort(set, nset, sizeof(int), cmp_row);
    }
    
    *selset = set;
    return nset;
}

/* Evaluate node recursively.
 *
 * Returns: 
 *    NODE_NULL  result/value is unknown   
 *    NODE_TRUE   
 *    NODE_FALSE  
 *    NODE_VALUE result is a value stored in 'value' 
 *               (if value is not NULL otherwise NODE_NULL is returned and value is not set)
 *    NODE_ERROR e.g. division by 0
 *
 * If results is NODE_VALUE, the 'value' is set, if value is type SQLP_S the string is not duplicated
 * and only pointer is set -> do not free value->s 
 */
double eval_node(SQLPNODE *nptr, int tab, int row, SQLPVALUE *value)
{
    int    left, right;
    SQLPVALUE left_value, right_value;
    int    ccol;
    COLUMN *col;
    VALUE  *val;
    double left_dval, right_dval, dval;

    /* Note: node types were previously checked by eval_node_type */

    G_debug ( 4, "eval_node node_type = %d", nptr->node_type );

    switch ( nptr->node_type) {
	case SQLP_NODE_VALUE:
	    if ( nptr->value.type == SQLP_NULL )
		return NODE_NULL;
	    
	    value->type = nptr->value.type;
	    value->s = nptr->value.s;
	    value->i = nptr->value.i;
	    value->d = nptr->value.d;
	    return NODE_VALUE;
	    break;

	case SQLP_NODE_COLUMN:
	    ccol = find_column(tab, nptr->column_name);
	    col = &(db.tables[tab].cols[ccol]);
	    val = &(db.tables[tab].rows[row].values[ccol]);

	    if ( val->is_null )
		return NODE_NULL;

	    switch (col->type) {
		case DBF_CHAR:
		    value->s = val->c; 
	    	    value->type = SQLP_S;
		    break;
		case DBF_INT:
		    value->i = val->i;
	    	    value->type = SQLP_I;
		    break;
		case DBF_DOUBLE:
		    value->d = val->d;
	    	    value->type = SQLP_D;
		break;
	    }
	    return NODE_VALUE;
	    break;

	case SQLP_NODE_EXPRESSION:
	    /* Note: Some expressions (e.g. NOT) have only one side */
	    if ( nptr->left ) {
	        left = eval_node ( nptr->left, tab, row, &left_value);
		G_debug ( 4, "    left = %d", left );

		if ( left == NODE_ERROR ) 
		    return NODE_ERROR;

		if ( left != NODE_NULL ) {
		    if ( left_value.type == SQLP_I )
			left_dval = left_value.i;
		    else
			left_dval = left_value.d;
		
		    G_debug ( 4, "    left_dval = %f", left_dval );
		}
	    }

	    if ( nptr->right ) {
	        right = eval_node ( nptr->right, tab, row, &right_value);
		G_debug ( 4, "    right = %d", right );

		if ( right == NODE_ERROR ) 
		    return NODE_ERROR;

		if ( right != NODE_NULL ) {
		    if ( right_value.type == SQLP_I )
			right_dval = right_value.i;
		    else
			right_dval = right_value.d;
		    
		    G_debug ( 4, "    right_dval = %f", right_dval );
		}
	    }
    
	    G_debug ( 4, "    operator = %d", nptr->oper );

	    switch ( nptr->oper ) {
		/* Arithmetical */
		case SQLP_ADD: 
		case SQLP_SUBTR: 
		case SQLP_MLTP: 
		case SQLP_DIV: 
		    if ( left == NODE_NULL || right == NODE_NULL )
			return NODE_NULL;

		    switch ( nptr->oper ) {
			case SQLP_ADD:	    
			    dval = left_dval + right_dval;		
			    break;
			case SQLP_SUBTR:
			    dval = left_dval - right_dval;		
			    break;
			case SQLP_MLTP:
			    dval = left_dval * right_dval;		
			    break;
			case SQLP_DIV:
			    if ( right_dval != 0.0) {
			        dval = left_dval / right_dval;		
			    } else {
			        append_error ("Division by zero\n");
			        return NODE_ERROR;
			    }		
			    break;
		    }
		    
		    if ( left_value.type == SQLP_I && right_value.type == SQLP_I && 
			 ( nptr->oper == SQLP_ADD || nptr->oper == SQLP_SUBTR ||  nptr->oper == SQLP_MLTP ) ) 
		    {
			value->type = SQLP_I;
			value->i = (int) dval;
		    } else { 
			value->type = SQLP_D;
			value->d = dval;
		    }
		    return NODE_VALUE;

		    break;

		/* Comparison */
		    /* Operators valid for all type */
		case SQLP_EQ:
		    if ( left == NODE_NULL || right == NODE_NULL ) {
			return NODE_NULL;
		    } else if ( left_value.type == SQLP_S ) { /* we checked before if right is also string */
			if ( left_value.s && right_value.s && strcmp(left_value.s,right_value.s) == 0)
			   return NODE_TRUE;
			else
			    return NODE_FALSE;
		    } else { /* numbers */
			if ( left_dval == right_dval )
			    return NODE_TRUE;
			else
			    return NODE_FALSE;
		    }
		    break;

		case SQLP_NE:
		    if ( left == NODE_NULL || right == NODE_NULL ) {
			return NODE_NULL;
		    } else if ( left_value.type == SQLP_S ) { /* we checked before if right is also string */
			if ( left_value.s && right_value.s && strcmp(left_value.s,right_value.s) != 0)
			   return NODE_TRUE;
			else
			    return NODE_FALSE;
		    } else { /* numbers */
			if ( left_dval != right_dval )
			    return NODE_TRUE;
			else
			    return NODE_FALSE;
		    }

		    /* Operators valid for numbers */
		case SQLP_LT:
		    if ( left == NODE_NULL || right == NODE_NULL ) {
			return NODE_NULL;
		    } else {
			if ( left_dval < right_dval )
			    return NODE_TRUE;
			else
			    return NODE_FALSE;
		    }

		case SQLP_LE:
		    if ( left == NODE_NULL || right == NODE_NULL ) {
			return NODE_NULL;
		    } else {
			if ( left_dval <= right_dval )
			    return NODE_TRUE;
			else
			    return NODE_FALSE;
		    }

		case SQLP_GT:
		    if ( left == NODE_NULL || right == NODE_NULL ) {
			return NODE_NULL;
		    } else {
			if ( left_dval > right_dval )
			    return NODE_TRUE;
			else
			    return NODE_FALSE;
		    }

		case SQLP_GE:
		    if ( left == NODE_NULL || right == NODE_NULL ) {
			return NODE_NULL;
		    } else {
			if ( left_dval >= right_dval )
			    return NODE_TRUE;
			else
			    return NODE_FALSE;
		    }

		    /* Operator valid for string */
		case SQLP_MTCH:
		    if ( left == NODE_NULL || right == NODE_NULL ) {
			return NODE_NULL;
		    } else {
			if ( left_value.s && right_value.s && strstr(left_value.s,right_value.s) != NULL) 
			    return NODE_TRUE;
			else
			    return NODE_FALSE;
		    }

		case SQLP_ISNULL:
		    return right == NODE_NULL ? NODE_TRUE : NODE_FALSE;

		case SQLP_NOTNULL:
		    return right != NODE_NULL ? NODE_TRUE : NODE_FALSE;

		/* Logical */
		case SQLP_AND:
		    if ( left == NODE_NULL || right == NODE_NULL ) {
			return NODE_NULL;
		    } else if ( left == NODE_TRUE && right == NODE_TRUE ) {
			return NODE_TRUE;
		    } else if ( left == NODE_VALUE || right == NODE_VALUE ) { /* Should not happen */
	    	    	append_error ("Value operand for AND\n");
			return NODE_ERROR;
		    } else {
			return NODE_FALSE;
		    }
		case SQLP_OR:
		    if ( left == NODE_NULL && right == NODE_NULL ) {
			return NODE_NULL;
		    } else if ( left == NODE_TRUE || right == NODE_TRUE ) {
			return NODE_TRUE;
		    } else if ( left == NODE_VALUE || right == NODE_VALUE ) { /* Should not happen */
	    	    	append_error ("Value operand for OR\n");
			return NODE_ERROR;
		    } else {
			return NODE_FALSE;
		    }
		case SQLP_NOT:
		    /* sub node stored on the right side */
		    if ( right == NODE_NULL ) {
			return NODE_NULL;
		    } else if ( right == NODE_TRUE ) {
			return NODE_FALSE;
		    } else if ( right == NODE_VALUE ) { /* Should not happen */
	    	    	append_error ("Value operand for NOT\n");
			return NODE_ERROR;
		    } else {
			return NODE_TRUE;
		    }

		default:
	    	    append_error ("Unknown operator %d\n", nptr->oper);
		    return NODE_FALSE;
	    }
    }
    
    return NODE_ERROR; /* Not reached */
}

/* Recursively get value/expression type.
 * Returns: node type (SQLP_S, SQLP_I, SQLP_D, SQLP_NULL, SQLP_BOOL)
 *          -1 on error (if types in expression are not compatible) 
 *
 * Rules:
 *      Values (in SQL Statement):
 *        SQLP_S              -> SQLP_S
 *        SQLP_I              -> SQLP_I
 *        SQLP_D              -> SQLP_D
 *        SQLP_NULL           -> SQLP_NULL
 *      Columns (in dbf table):
 *        DBF_CHAR            -> SQLP_S
 *        DBF_INT             -> SQLP_I
 *        DBF_DOUBLE          -> SQLP_D
 *      Arithetical Expressions :
 *        side1   side2           exp  
 *        SQLP_S    ALL           ALL    -> error
 *        SQLP_NULL SQLP_I        ALL    -> SQLP_NULL
 *        SQLP_NULL SQLP_D        ALL    -> SQLP_NULL
 *        SQLP_I    SQLP_I        +,-,*  -> SQLP_I
 *        SQLP_I    SQLP_I        /      -> SQLP_D
 *        SQLP_I    SQLP_D        ALL    -> SQLP_D
 *        SQLP_D    SQLP_D        ALL    -> SQLP_D
 *      Comparisons :
 *        side1     side2     exp  
 *        SQLP_S    SQLP_S    =,<>,~          -> SQLP_BOOL
 *        SQLP_S    SQLP_S    <,<=,>,>=       -> error
 *        SQLP_S    SQLP_I    ALL             -> error
 *        SQLP_S    SQLP_D    ALL             -> error
 *        SQLP_I    SQLP_I    =,<>,<,<=,>,>=  -> SQLP_BOOL
 *        SQLP_D    SQLP_D    =,<>,<,<=,>,>=  -> SQLP_BOOL
 *        SQLP_I    SQLP_D    =,<>,<,<=,>,>=  -> SQLP_BOOL
 *        SQLP_I    ALL       ~               -> error
 *        SQLP_D    ALL       ~               -> error
 *        SQLP_NULL ALL       ALL             -> SQLP_NULL
 *      Logical expressions 
 *        In general, if we know that the result is NULL regardless actual values it returns SQLP_NULL
 *        so that tests for individual rows are not performed, otherwise SQLP_BOOL
 *        SQLP_BOOL SQLP_BOOL AND             	-> SQLP_BOOL
 *        SQLP_BOOL SQLP_NULL AND             	-> SQLP_NULL
 *        SQLP_NULL SQLP_NULL AND             	-> SQLP_NULL
 *        SQLP_BOOL SQLP_BOOL OR		-> SQLP_BOOL
 *        SQLP_BOOL SQLP_NULL OR		-> SQLP_BOOL
 *        SQLP_NULL SQLP_NULL OR		-> SQLP_NULL
 *        SQLP_BOOL -         NOT		-> SQLP_BOOL
 *        SQLP_NULL -         NOT		-> SQLP_NULL
 */
int eval_node_type(SQLPNODE *nptr, int tab ) {
    int left, right;
    int ccol;
    COLUMN *col = NULL;

    switch ( nptr->node_type) {
	case SQLP_NODE_VALUE:
	    return nptr->value.type;
	    break;

	case SQLP_NODE_COLUMN:
	    ccol = find_column ( tab, nptr->column_name );
	    if ( ccol == -1 ) {
		append_error ("Column '%s' not found\n", nptr->column_name);
		return (-1);
	    }
	    col = &(db.tables[tab].cols[ccol]);
	    switch (col->type) {
		case DBF_CHAR:
		    return (SQLP_S);
		    break;
		case DBF_INT:
		    return (SQLP_I);
		    break;
		case DBF_DOUBLE:
		    return (SQLP_D);
		    break;
	    }
	    break;

	case SQLP_NODE_EXPRESSION:
	    /* Note: Some expressions (e.g. NOT) have only one side */
	    if ( nptr->left ) {
	        left = eval_node_type( nptr->left, tab);
		if ( left == -1 ) 
		    return -1;
	    }

	    if ( nptr->right ) {
	        right = eval_node_type( nptr->right, tab);
		if ( right == -1 ) 
		    return -1;
	    }

	    switch ( nptr->oper ) {
		/* Arithmetical */
		case SQLP_ADD: 
		case SQLP_SUBTR: 
		case SQLP_MLTP: 
		case SQLP_DIV: 
		    if ( left == SQLP_S || right == SQLP_S ) {
		        append_error ("Arithmetical operation with strings is not allowed\n" );	
			return -1;
		    } else if ( left == SQLP_NULL || right == SQLP_NULL ) {
			return SQLP_NULL;
		    } else if ( left == SQLP_I && right == SQLP_I && ( nptr->oper == SQLP_ADD ||  
				nptr->oper == SQLP_SUBTR ||  nptr->oper == SQLP_MLTP ) ) 
		    {
			return SQLP_I;
		    } else { 
			return SQLP_D;
		    }
		    break;

		/* Comparison */
		    /* Operators valid for all type */
		case SQLP_EQ:
		case SQLP_NE:
		    if ( ( left  == SQLP_S && ( right == SQLP_I || right == SQLP_D ) ) ||
		         ( right == SQLP_S && ( left  == SQLP_I || left  == SQLP_D ) ) )
		    {
		        append_error ("Comparison between string and number is not allowed\n" );	
			return -1;
		    } else if ( left == SQLP_NULL || right == SQLP_NULL ) {
			return SQLP_NULL;
		    } else {
			return SQLP_BOOL;
		    }
		    /* Operators valid for numbers */
		case SQLP_LT:
		case SQLP_LE:
		case SQLP_GT:
		case SQLP_GE:
		    if ( left  == SQLP_S || right == SQLP_S ) {
			append_error ("Comparison '%s' between strings not allowed\n", 
				       sqpOperatorName(nptr->oper) );
			return -1;
		    } else if ( left == SQLP_NULL || right == SQLP_NULL ) { 
			return SQLP_NULL;
		    } else {
			return SQLP_BOOL;
		    }
		    /* Operator valid for string */
		case SQLP_MTCH:
		    if ( left == SQLP_I || left == SQLP_D || right == SQLP_I || right == SQLP_D ) {
			append_error ("Match (~) between numbers not allowed\n" );
			return -1;
		    } else if ( left == SQLP_NULL || right == SQLP_NULL ) {
			return SQLP_NULL;
		    } else {
			return SQLP_BOOL;
		    }

		case SQLP_ISNULL:
		case SQLP_NOTNULL:
		    return SQLP_BOOL;

		/* Logical */
		case SQLP_AND:
		    if ( left == SQLP_NULL || right == SQLP_NULL ) {
			return SQLP_NULL;
		    } else { 
			return SQLP_BOOL;
		    }
		case SQLP_OR:
		    if ( left == SQLP_NULL && right == SQLP_NULL ) {
			return SQLP_NULL;
		    } else { 
			return SQLP_BOOL;
		    }
		case SQLP_NOT:
		    /* sub node stored on the right side */
		    if ( right == SQLP_NULL ) {
			return SQLP_NULL;
		    } else { 
			return SQLP_BOOL;
		    }

		default:
	    	    append_error ("Unknown operator %d\n", nptr->oper);
		    return -1;
	    }
    }
    
    return -1; /* Not reached */ 
}