update.c

在VC6环境下开发

#include "eDbInit.h"
/*
** Process an UPDATE statement.
**
**   UPDATE  table_wxyz SET a=b, c=d WHERE e<5 AND f NOT NULL;
**           \________/     \______/       \________________/
*             pTabList      pChanges             pWhere
*/
void eDbUpdate(
	Parser *pParse,         /* The parser context */
	SrcList *pTabList,     /* The table in which we should change things */
	IdExprList *pChanges,  /* Things to be changed */
	Expr *pWhere           /* The WHERE clause.  May be null */
){
	int i, j;              /* Loop counters */
	Table *pTab;           /* The table to be updated */
	Index *pIdx;           /* For looping over indices */
	int iCur;              /* VDBE Cursor number of pTab */
	eDb *db;            /* The database structure */
	int *aXRef = 0;        /* aXRef[i] is the index in pChanges->a[] of the
						 ** an expression for the i-th column of the table.
						 ** aXRef[i]==-1 if the i-th column is not changed. */
	int keyColumn;         /* True if the record number is being changed */
	int isView;            /* Trying to update a view */
	ExprList *pEList;
	IdList *pIdList;

	ParseResult *pRes = eDbMalloc(sizeof(ParseResult));

	if( pParse->nErr || eDb_malloc_failed ) goto update_cleanup;
	db = pParse->db;
	assert( pTabList->nSrc==1 );

	/* Locate the table which we want to update. 
	*/
	pTab = eDbSrcListLookup(pParse, pTabList);
	if( pTab==0 ) goto update_cleanup;
	isView = pTab->pSelect!=0;	
	aXRef = eDbMalloc( sizeof(u8) * pTab->nCol );
	if( aXRef==0 ) goto update_cleanup;
	for(i=0; i<pTab->nCol; i++) aXRef[i] = -1;
	
	/* Allocate a cursors for the main database table and for all indices.
	** The index cursors might not be used, but if they are used they
	** need to occur right after the database cursor.  So go ahead and
	** allocate enough space, just in case.
	*/
	pTabList->a[0].iCursor = iCur = pParse->nTab++;
	for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
		pParse->nTab++;
	}

	/* Resolve the column names in all the expressions of the
	** of the UPDATE statement.  Also find the column index
	** for each column to be updated in the pChanges array.
	*/
	pIdList = pChanges->pIdList;
	pEList = pChanges->pEList;

	for(i=0; i<pEList->nExpr; i++){
		if( eDbExprResolveIds(pParse, pTabList, 0, pEList->a[i].pExpr) ){
			goto update_cleanup;
		}
		if( eDbExprCheck(pParse, pEList->a[i].pExpr, 0, 0) ){
			goto update_cleanup;
		}
	}
	
	for(i=0; i<pIdList->nId; i++){
		pIdList->a[i].idx = -1;
	}

	for(i=0; i<pIdList->nId; i++){
		/*find the column name in table and set its indices */
		for(j=0; j<pTab->nCol; j++){
			if( eDbStrICmp(pIdList->a[i].zName, pTab->aCol[j].zName)==0 ){
				pIdList->a[i].idx = j;
				if( j==pTab->iPKey ){
					keyColumn = i;
				}
				break;
			}
		}
		if( j>=pTab->nCol ){
			eDbErrorMsg(pParse, "table %s has no column named %s",
			  pTabList->a[0].zName, 0, pIdList->a[i].zName);
			pParse->nErr++;
			goto update_cleanup;
		}
	} 
	/* Resolve the column names in all the expressions in the
	** WHERE clause.
	*/
	if( pWhere ){
		if( eDbExprResolveIds(pParse, pTabList, 0, pWhere) ){
			goto update_cleanup;
		}
		if( eDbExprCheck(pParse, pWhere, 0, 0) ){
			goto update_cleanup;
		}
		eDbDealwithWhereClause(pTabList,pWhere);
	}
	/* Special case: A DELETE without a WHERE clause deletes everything.
	** It is easier just to erase the whole table.  Note, however, that
	** this means that the row change count will be incorrect.
	*/	
	else{		
	}
	pRes->pWhere = pWhere;
	pRes->pTable = pTab;
	pRes->pIdList = pIdList;
	pRes->pEList = pEList;
	pRes->op = Op_Update;
	pParse->pResult = pRes;
	eDbSrcListDelete(pTabList);
	return;
update_cleanup:
	eDbFree(aXRef);
	eDbSrcListDelete(pTabList);
	eDbIdExprListDelete(pChanges);
	eDbExprDelete(pWhere);
	return;
}