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Comment fixes and improvements in sqlite3ProcessJoin().

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FossilOrigin-Name: 1118655f4d58da1273e83954c80d8bc17fa3bde7a39e81cb9947d59894d5ab93
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drh
2022-04-20 16:26:22 +00:00
parent 815b782e99
commit bc656e220f
3 changed files with 20 additions and 13 deletions
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19
src/select.c
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@@ -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.