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Overview
Comment:Improvements to comments. No code changes.
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SHA1: 4165d20f64d778a4e48f511a37cfced8579d4dbe
User & Date: drh 2016-08-20 01:06:22
Context
2016-08-20
12:00
Improvements to the vector comparison splitter in exprAnalyze(). check-in: a3ffd283 user: drh tags: rowvalue
01:06
Improvements to comments. No code changes. check-in: 4165d20f user: drh tags: rowvalue
00:51
Add support for vector assignments in the SET clause of an UPDATE statement. check-in: f320d47d user: drh tags: rowvalue
Changes
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Changes to src/expr.c.

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#endif /* !defined(SQLITE_OMIT_SUBQUERY) */

#ifndef SQLITE_OMIT_SUBQUERY
/*
** Compute and return a new Expr object which when passed to
** sqlite3ExprCode() will generate all necessary code to compute
** the iField-th column of the vector expression pVector.



**
** The caller owns the returned Expr object and is responsible for
** ensuring that the returned value eventually gets freed.
**
** The caller retains ownership of pVector and must ensure that pVector
** remains valid as long as the returned value is in use.







*/
Expr *sqlite3ExprForVectorField(
  Parse *pParse,       /* Parsing context */
  Expr *pVector,       /* The vector.  List of expressions or a sub-SELECT */
  int iField           /* Which column of the vector to return */
){
  Expr *pRet;
  if( pVector->op==TK_SELECT ){
    assert( pVector->flags & EP_xIsSelect );
    /* The TK_SELECT_COLUMN Expr node:
    **
    ** pLeft:           pVector containing TK_SELECT
    ** pRight:          pVector if ownership taken
    ** iColumn:         Index of a column in pVector
    ** pLeft->iTable:   First in an array of register holding result, or 0
    **                  if the result is not yet computed.
    **
    ** sqlite3ExprDelete() specifically skips the recursive delete of
    ** pLeft on TK_SELECT_COLUMN nodes.  But pRight is followed, so pVector
    ** is included on pRight if ownership is taken.  Typically there will
    ** be multiple TK_SELECT_COLUMN nodes with the same pLeft pointer to 

    ** the pVector, but only one of them will own the pVector.
    */
    pRet = sqlite3PExpr(pParse, TK_SELECT_COLUMN, pVector, 0, 0);
    if( pRet ) pRet->iColumn = iField;
    assert( pRet==0 || pRet->iTable==0 );
  }else{
    if( pVector->op==TK_VECTOR ) pVector = pVector->x.pList->a[iField].pExpr;
    pRet = sqlite3ExprDup(pParse->db, pVector, 0);
................................................................................
  /* Avoid leaking memory if malloc has failed. */
  sqlite3ExprDelete(db, pExpr);
  sqlite3ExprListDelete(db, pList);
  return 0;
}

/*
** pColumns and pExpr for a vector assignment, like this:

**
**        (a,b,c) = (expr1,expr2,expr3)
** Or:    (a,b,c) = (SELECT x,y,z FROM ....)
**
** For each term of the vector assignment, append new entries to the
** expression list.  In the case of a subquery on the LHS, append
** TK_SELECT_COLUMN expressions.
*/
ExprList *sqlite3ExprListAppendVector(
  Parse *pParse,         /* Parsing context */
  ExprList *pList,       /* List to which to append. Might be NULL */
  IdList *pColumns,      /* List of names of LHS of the assignment */
  Expr *pExpr            /* Vector expression to be appended. Might be NULL */







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#endif /* !defined(SQLITE_OMIT_SUBQUERY) */

#ifndef SQLITE_OMIT_SUBQUERY
/*
** Compute and return a new Expr object which when passed to
** sqlite3ExprCode() will generate all necessary code to compute
** the iField-th column of the vector expression pVector.
**
** It is ok for pVector to be a scalar (as long as iField==0).  
** In that case, this routine works like sqlite3ExprDup().
**
** The caller owns the returned Expr object and is responsible for
** ensuring that the returned value eventually gets freed.
**
** The caller retains ownership of pVector.  If pVector is a TK_SELECT,
** then the return value will reference pVector and so pVector must remain
** valid for the life of the returned object.  If pVector is a TK_VECTOR
** or a scalar expression, then it can be deleted as soon as this routine
** routines.
**
** A trick to cause a TK_SELECT pVector to be deleted together with
** the returned Expr object is to attach the pVector to the pRight field
** of the returned TK_SELECT_COLUMN Expr object.
*/
Expr *sqlite3ExprForVectorField(
  Parse *pParse,       /* Parsing context */
  Expr *pVector,       /* The vector.  List of expressions or a sub-SELECT */
  int iField           /* Which column of the vector to return */
){
  Expr *pRet;
  if( pVector->op==TK_SELECT ){
    assert( pVector->flags & EP_xIsSelect );
    /* The TK_SELECT_COLUMN Expr node:
    **
    ** pLeft:           pVector containing TK_SELECT
    ** pRight:          not used.  But recursively deleted.
    ** iColumn:         Index of a column in pVector
    ** pLeft->iTable:   First in an array of register holding result, or 0
    **                  if the result is not yet computed.
    **
    ** sqlite3ExprDelete() specifically skips the recursive delete of
    ** pLeft on TK_SELECT_COLUMN nodes.  But pRight is followed, so pVector
    ** can be attached to pRight to cause this node to take ownership of
    ** pVector.  Typically there will be multiple TK_SELECT_COLUMN nodes
    ** with the same pLeft pointer to the pVector, but only one of them
    ** will own the pVector.
    */
    pRet = sqlite3PExpr(pParse, TK_SELECT_COLUMN, pVector, 0, 0);
    if( pRet ) pRet->iColumn = iField;
    assert( pRet==0 || pRet->iTable==0 );
  }else{
    if( pVector->op==TK_VECTOR ) pVector = pVector->x.pList->a[iField].pExpr;
    pRet = sqlite3ExprDup(pParse->db, pVector, 0);
................................................................................
  /* Avoid leaking memory if malloc has failed. */
  sqlite3ExprDelete(db, pExpr);
  sqlite3ExprListDelete(db, pList);
  return 0;
}

/*
** pColumns and pExpr form a vector assignment which is part of the SET
** clause of an UPDATE statement.  Like this:
**
**        (a,b,c) = (expr1,expr2,expr3)
** Or:    (a,b,c) = (SELECT x,y,z FROM ....)
**
** For each term of the vector assignment, append new entries to the
** expression list pList.  In the case of a subquery on the LHS, append
** TK_SELECT_COLUMN expressions.
*/
ExprList *sqlite3ExprListAppendVector(
  Parse *pParse,         /* Parsing context */
  ExprList *pList,       /* List to which to append. Might be NULL */
  IdList *pColumns,      /* List of names of LHS of the assignment */
  Expr *pExpr            /* Vector expression to be appended. Might be NULL */