database/sqlite
1
0
Fork 0
mirror of https://github.com/sqlite/sqlite.git synced 2025-11-12 13:01:09 +03:00
Code Activity

Clarification and simplification and result column naming logic.

Browse Source 
FossilOrigin-Name: 68824a439b76a4cca05609a02de7abdc42bd1d26afbfcd047b90001c610d3c56
This commit is contained in:
drh
2017-07-12 14:10:19 +00:00
parent 47ebd4cadd
commit ec360a8d01
3 changed files with 59 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

71
src/select.c
View File

@@ -1568,20 +1568,46 @@ static Table *tableWithCursor(SrcList *pList, int iCursor){
/*
** Generate code that will tell the VDBE the names of columns
** in the result set. This information is used to provide the
** azCol[] values in the callback.
** Compute the column names for a SELECT statement.
**
** The only guarantee that SQLite makes about column names is that if the
** column has an AS clause assigning it a name, that will be the name used.
** That is the only documented guarantee. However, countless applications
** developed over the years have made baseless assumptions about column names
** and will break if those assumptions changes. Hence, use extreme caution
** when modifying this routine to avoid breaking legacy.
**
** See Also: sqlite3ColumnsFromExprList()
**
** The PRAGMA short_column_names and PRAGMA full_column_names settings are
** deprecated. The default setting is short=ON, full=OFF. 99.9% of all
** applications should operate this way. Nevertheless, we need to support the
** other modes for legacy:
**
** short=OFF, full=OFF: Column name is the text of the expression has it
** originally appears in the SELECT statement. In
** other words, the zSpan of the result expression.
**
** short=ON, full=OFF: (This is the default setting). If the result
** refers directly to a table column, then the result
** column name is just the table column name: COLUMN.
** Otherwise use zSpan.
**
** full=ON, short=ANY: If the result refers directly to a table column,
** then the result column name with the table name
** prefix, ex: TABLE.COLUMN. Otherwise use zSpan.
*/
static void generateColumnNames(
Parse *pParse, /* Parser context */
SrcList *pTabList, /* List of tables */
SrcList *pTabList, /* The FROM clause of the SELECT */
ExprList *pEList /* Expressions defining the result set */
){
Vdbe *v = pParse->pVdbe;
int i;
Table *pTab;
sqlite3 *db = pParse->db;
int fullNames, shortNames;
int fullName; /* TABLE.COLUMN if no AS clause and is a direct table ref */
int srcName; /* COLUMN or TABLE.COLUMN if no AS clause and is direct */
#ifndef SQLITE_OMIT_EXPLAIN
/* If this is an EXPLAIN, skip this step */
@@ -1594,17 +1620,19 @@ static void generateColumnNames(
assert( v!=0 );
assert( pTabList!=0 );
pParse->colNamesSet = 1;
fullNames = (db->flags & SQLITE_FullColNames)!=0;
shortNames = (db->flags & SQLITE_ShortColNames)!=0;
fullName = (db->flags & SQLITE_FullColNames)!=0;
srcName = (db->flags & SQLITE_ShortColNames)!=0 || fullName;
sqlite3VdbeSetNumCols(v, pEList->nExpr);
for(i=0; i<pEList->nExpr; i++){
Expr *p;
p = pEList->a[i].pExpr;
if( NEVER(p==0) ) continue;
Expr *p = pEList->a[i].pExpr;
assert( p!=0 );
if( pEList->a[i].zName ){
/* An AS clause always takes first priority */
char *zName = pEList->a[i].zName;
sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_TRANSIENT);
}else if( (p->op==TK_COLUMN || p->op==TK_AGG_COLUMN)
}else if( srcName
&& (p->op==TK_COLUMN || p->op==TK_AGG_COLUMN)
&& (pTab = tableWithCursor(pTabList, p->iTable))!=0
){
char *zCol;
@@ -1616,10 +1644,7 @@ static void generateColumnNames(
}else{
zCol = pTab->aCol[iCol].zName;
}
if( !shortNames && !fullNames ){
sqlite3VdbeSetColName(v, i, COLNAME_NAME,
sqlite3DbStrDup(db, pEList->a[i].zSpan), SQLITE_DYNAMIC);
}else if( fullNames ){
if( fullName ){
char *zName = 0;
zName = sqlite3MPrintf(db, "%s.%s", pTab->zName, zCol);
sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_DYNAMIC);
@@ -1647,6 +1672,15 @@ static void generateColumnNames(
**
** Return SQLITE_OK on success. If a memory allocation error occurs,
** store NULL in *paCol and 0 in *pnCol and return SQLITE_NOMEM.
**
** The only guarantee that SQLite makes about column names is that if the
** column has an AS clause assigning it a name, that will be the name used.
** That is the only documented guarantee. However, countless applications
** developed over the years have made baseless assumptions about column names
** and will break if those assumptions changes. Hence, use extreme caution
** when modifying this routine to avoid breaking legacy.
**
** See Also: generateColumnNames()
*/
int sqlite3ColumnsFromExprList(
Parse *pParse, /* Parsing context */
@@ -1659,7 +1693,6 @@ int sqlite3ColumnsFromExprList(
u32 cnt; /* Index added to make the name unique */
Column *aCol, *pCol; /* For looping over result columns */
int nCol; /* Number of columns in the result set */
Expr *p; /* Expression for a single result column */
char *zName; /* Column name */
int nName; /* Size of name in zName[] */
Hash ht; /* Hash table of column names */
@@ -1680,12 +1713,10 @@ int sqlite3ColumnsFromExprList(
for(i=0, pCol=aCol; i<nCol && !db->mallocFailed; i++, pCol++){
/* Get an appropriate name for the column
*/
p = sqlite3ExprSkipCollate(pEList->a[i].pExpr);
if( (zName = pEList->a[i].zName)!=0 ){
/* If the column contains an "AS <name>" phrase, use <name> as the name */
}else{
Expr *pColExpr = p; /* The expression that is the result column name */
Table *pTab; /* Table associated with this expression */
Expr *pColExpr = sqlite3ExprSkipCollate(pEList->a[i].pExpr);
while( pColExpr->op==TK_DOT ){
pColExpr = pColExpr->pRight;
assert( pColExpr!=0 );
@@ -1693,7 +1724,7 @@ int sqlite3ColumnsFromExprList(
if( pColExpr->op==TK_COLUMN && pColExpr->pTab!=0 ){
/* For columns use the column name name */
int iCol = pColExpr->iColumn;
pTab = pColExpr->pTab;
Table *pTab = pColExpr->pTab;
if( iCol<0 ) iCol = pTab->iPKey;
zName = iCol>=0 ? pTab->aCol[iCol].zName : "rowid";
}else if( pColExpr->op==TK_ID ){