diff options
Diffstat (limited to 'src/select.c')
| -rw-r--r-- | src/select.c | 19 |
1 files changed, 13 insertions, 6 deletions
diff --git a/src/select.c b/src/select.c index 3f754915d..c86ae1f52 100644 --- a/src/select.c +++ b/src/select.c @@ -456,15 +456,22 @@ static void unsetJoinExpr(Expr *p, int iTable){ /* ** This routine processes the join information for a SELECT statement. -** ON and USING clauses are converted into extra terms of the WHERE clause. -** NATURAL joins also create extra WHERE clause terms. +** +** * A NATURAL join is converted into a USING join. After that, we +** do not need to be concerned with NATURAL joins and we only have +** think about USING joins. +** +** * ON and USING clauses result in extra terms being added to the +** WHERE clause to enforce the specified constraints. The extra +** WHERE clause terms will be tagged with EP_FromJoin or +** EP_InnerJoin so that we know that they originated in ON/USING. ** ** The terms of a FROM clause are contained in the Select.pSrc structure. ** The left most table is the first entry in Select.pSrc. The right-most ** table is the last entry. The join operator is held in the entry to -** the left. Thus entry 0 contains the join operator for the join between +** the right. Thus entry 1 contains the join operator for the join between ** entries 0 and 1. Any ON or USING clauses associated with the join are -** also attached to the left entry. +** also attached to the right entry. ** ** This routine returns the number of errors encountered. */ @@ -551,8 +558,8 @@ static int sqlite3ProcessJoin(Parse *pParse, Select *p){ if( (pSrc->a[0].fg.jointype & JT_LTORJ)!=0 ){ /* This branch runs if the query contains one or more RIGHT or FULL ** JOINs. If only a single table on the left side of this join - ** contains the zName column, then this routine is branch is - ** a no-op. But if there are two or more tables on the left side + ** contains the zName column, then this branch is a no-op. + ** But if there are two or more tables on the left side ** of the join, construct a coalesce() function that gathers all ** such tables. Raise an error if more than one of those references ** to zName is not also within a prior USING clause. |