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Enhance the use of the column cache for UPDATE statements, making them

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more efficient for the case where a column is modified to be an expression
of other unmodified columns.

FossilOrigin-Name: 871e091df651b2275a672c35ff938bd4b6db0d7f
This commit is contained in:
drh
2015-10-15 19:21:51 +00:00
parent fed7ac6f04
commit ce78bc6e7e
7 changed files with 34 additions and 28 deletions
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22
src/expr.c
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@@ -2481,9 +2481,12 @@ void sqlite3ExprCodeGetColumnOfTable(
/*
** Generate code that will extract the iColumn-th column from
** table pTab and store the column value in a register. An effort
** is made to store the column value in register iReg, but this is
** not guaranteed. The location of the column value is returned.
** table pTab and store the column value in a register.
**
** An effort is made to store the column value in register iReg. This
** is not garanteeed for GetColumn() - the result can be stored in
** any register. But the result is guaranteed to land in register iReg
** for GetColumnToReg().
**
** There must be an open cursor to pTab in iTable when this routine
** is called. If iColumn<0 then code is generated that extracts the rowid.
@@ -2494,7 +2497,7 @@ int sqlite3ExprCodeGetColumn(
int iColumn, /* Index of the table column */
int iTable, /* The cursor pointing to the table */
int iReg, /* Store results here */
u8 p5 /* P5 value for OP_Column */
u8 p5 /* P5 value for OP_Column + FLAGS */
){
Vdbe *v = pParse->pVdbe;
int i;
@@ -2516,6 +2519,17 @@ int sqlite3ExprCodeGetColumn(
}
return iReg;
}
void sqlite3ExprCodeGetColumnToReg(
Parse *pParse, /* Parsing and code generating context */
Table *pTab, /* Description of the table we are reading from */
int iColumn, /* Index of the table column */
int iTable, /* The cursor pointing to the table */
int iReg /* Store results here */
){
int r1 = sqlite3ExprCodeGetColumn(pParse, pTab, iColumn, iTable, iReg, 0);
if( r1!=iReg ) sqlite3VdbeAddOp2(pParse->pVdbe, OP_SCopy, r1, iReg);
}
/*
** Clear all column cache entries.