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Improved comments on sqlite3CodeSubquery(). No changes to code.

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FossilOrigin-Name: acea4ee136def4815d22eec240c5903a72bde9bd
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drh
2016-08-19 19:12:58 +00:00
parent a15a8bc822
commit 39a11819f3
3 changed files with 25 additions and 16 deletions
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27
src/expr.c
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@@ -2211,7 +2211,9 @@ void sqlite3SubselectError(Parse *pParse, int nActual, int nExpect){
** value to non-NULL if the RHS is NULL-free.
**
** For a SELECT or EXISTS operator, return the register that holds the
** result. For IN operators or if an error occurs, the return value is 0.
** result. For a multi-column SELECT, the result is stored in a contiguous
** array of registers and the return value is the register of the left-most
** result column. Return 0 for IN operators or if an error occurs.
*/
#ifndef SQLITE_OMIT_SUBQUERY
int sqlite3CodeSubselect(
@@ -2226,8 +2228,8 @@ int sqlite3CodeSubselect(
if( NEVER(v==0) ) return 0;
sqlite3ExprCachePush(pParse);
/* This code must be run in its entirety every time it is encountered
** if any of the following is true:
/* The evaluation of the IN/EXISTS/SELECT must be repeated every time it
** is encountered if any of the following is true:
**
** * The right-hand side is a correlated subquery
** * The right-hand side is an expression list containing variables
@@ -2387,14 +2389,21 @@ int sqlite3CodeSubselect(
case TK_EXISTS:
case TK_SELECT:
default: {
/* If this has to be a scalar SELECT. Generate code to put the
** value of this select in a memory cell and record the number
** of the memory cell in iColumn. If this is an EXISTS, write
** an integer 0 (not exists) or 1 (exists) into a memory cell
** and record that memory cell in iColumn.
/* Case 3: (SELECT ... FROM ...)
** or: EXISTS(SELECT ... FROM ...)
**
** For a SELECT, generate code to put the values for all columns of
** the first row into an array of registers and return the index of
** the first register.
**
** If this is an EXISTS, write an integer 0 (not exists) or 1 (exists)
** into a register and return that register number.
**
** In both cases, the query is augmented with "LIMIT 1". Any
** preexisting limit is discarded in place of the new LIMIT 1.
*/
Select *pSel; /* SELECT statement to encode */
SelectDest dest; /* How to deal with SELECt result */
SelectDest dest; /* How to deal with SELECT result */
int nReg; /* Registers to allocate */
testcase( pExpr->op==TK_EXISTS );