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Initial implementation of the unlikely() SQL function used as a hint to

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the query planner.

FossilOrigin-Name: 036fc37a034093a4c6fc190633bd41c2b7230d77
This commit is contained in:
drh
2013-09-06 15:23:29 +00:00
parent d36e104112
commit cca9f3d291
8 changed files with 118 additions and 31 deletions
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20
src/func.c
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@@ -418,14 +418,14 @@ static void lowerFunc(sqlite3_context *context, int argc, sqlite3_value **argv){
}
/*
** The COALESCE() and IFNULL() functions are implemented as VDBE code so
** that unused argument values do not have to be computed. However, we
** still need some kind of function implementation for this routines in
** the function table. That function implementation will never be called
** so it doesn't matter what the implementation is. We might as well use
** the "version()" function as a substitute.
** Some functions like COALESCE() and IFNULL() and UNLIKELY() are implemented
** as VDBE code so that unused argument values do not have to be computed.
** However, we still need some kind of function implementation for this
** routines in the function table. The noopFunc macro provides this.
** noopFunc will never be called so it doesn't matter what the implementation
** is. We might as well use the "version()" function as a substitute.
*/
#define ifnullFunc versionFunc /* Substitute function - never called */
#define noopFunc versionFunc /* Substitute function - never called */
/*
** Implementation of random(). Return a random integer.
@@ -1659,9 +1659,11 @@ void sqlite3RegisterGlobalFunctions(void){
FUNCTION(lower, 1, 0, 0, lowerFunc ),
FUNCTION(coalesce, 1, 0, 0, 0 ),
FUNCTION(coalesce, 0, 0, 0, 0 ),
FUNCTION2(coalesce, -1, 0, 0, ifnullFunc, SQLITE_FUNC_COALESCE),
FUNCTION2(coalesce, -1, 0, 0, noopFunc, SQLITE_FUNC_COALESCE),
FUNCTION(hex, 1, 0, 0, hexFunc ),
FUNCTION2(ifnull, 2, 0, 0, ifnullFunc, SQLITE_FUNC_COALESCE),
FUNCTION2(ifnull, 2, 0, 0, noopFunc, SQLITE_FUNC_COALESCE),
FUNCTION2(unlikely, 1, 0, 0, noopFunc, SQLITE_FUNC_UNLIKELY),
FUNCTION2(unlikely, 2, 0, 0, noopFunc, SQLITE_FUNC_UNLIKELY),
FUNCTION(random, 0, 0, 0, randomFunc ),
FUNCTION(randomblob, 1, 0, 0, randomBlob ),
FUNCTION(nullif, 2, 0, 1, nullifFunc ),