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Overview
Comment:Generate VDBE code for the built-in COALESCE() and IFNULL() functions. This allows unused arguments to never be evaluated, which is a performance win when the unused argument is a subquery.
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SHA1:30055b257c3c65f8123cad5ac6c62c4c6ca2c900
User & Date: drh 2009-11-11 00:24:32
Context
2009-11-11
01:14
Additional test cases for the coalesce() and ifnull() functions. check-in: d0591258 user: drh tags: trunk
00:24
Generate VDBE code for the built-in COALESCE() and IFNULL() functions. This allows unused arguments to never be evaluated, which is a performance win when the unused argument is a subquery. check-in: 30055b25 user: drh tags: trunk
2009-11-10
17:55
Additional intarray test cases and tweaks to comments. check-in: 0c8db5d8 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/expr.c.

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      zId = pExpr->u.zToken;
      nId = sqlite3Strlen30(zId);
      pDef = sqlite3FindFunction(db, zId, nId, nFarg, enc, 0);
      if( pDef==0 ){
        sqlite3ErrorMsg(pParse, "unknown function: %.*s()", nId, zId);
        break;
      }





















      if( pFarg ){
        r1 = sqlite3GetTempRange(pParse, nFarg);
        sqlite3ExprCachePush(pParse);     /* Ticket 2ea2425d34be */
        sqlite3ExprCodeExprList(pParse, pFarg, r1, 1);
        sqlite3ExprCachePop(pParse, 1);   /* Ticket 2ea2425d34be */
      }else{
        r1 = 0;







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      zId = pExpr->u.zToken;
      nId = sqlite3Strlen30(zId);
      pDef = sqlite3FindFunction(db, zId, nId, nFarg, enc, 0);
      if( pDef==0 ){
        sqlite3ErrorMsg(pParse, "unknown function: %.*s()", nId, zId);
        break;
      }

      /* Attempt a direct implementation of the built-in COALESCE() and
      ** IFNULL() functions.  This avoids unnecessary evalation of
      ** arguments past the first non-NULL argument.
      */
      if( pDef->flags & SQLITE_FUNC_COALESCE ){
        int endCoalesce = sqlite3VdbeMakeLabel(v);
        assert( nFarg>=2 );
        sqlite3ExprCode(pParse, pFarg->a[0].pExpr, target);
        for(i=1; i<nFarg; i++){
          sqlite3VdbeAddOp2(v, OP_NotNull, target, endCoalesce);
          sqlite3ExprCacheRemove(pParse, target);
          sqlite3ExprCachePush(pParse);
          sqlite3ExprCode(pParse, pFarg->a[i].pExpr, target);
          sqlite3ExprCachePop(pParse, 1);
        }
        sqlite3VdbeResolveLabel(v, endCoalesce);
        break;
      }


      if( pFarg ){
        r1 = sqlite3GetTempRange(pParse, nFarg);
        sqlite3ExprCachePush(pParse);     /* Ticket 2ea2425d34be */
        sqlite3ExprCodeExprList(pParse, pFarg, r1, 1);
        sqlite3ExprCachePop(pParse, 1);   /* Ticket 2ea2425d34be */
      }else{
        r1 = 0;

Changes to src/func.c.

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        z1[i] = sqlite3Tolower(z1[i]);
      }
      sqlite3_result_text(context, (char *)z1, -1, sqlite3_free);
    }
  }
}









/*
** Implementation of the IFNULL(), NVL(), and COALESCE() functions.  
** All three do the same thing.  They return the first non-NULL
** argument.
*/
static void ifnullFunc(
  sqlite3_context *context,
................................................................................
  for(i=0; i<argc; i++){
    if( SQLITE_NULL!=sqlite3_value_type(argv[i]) ){
      sqlite3_result_value(context, argv[i]);
      break;
    }
  }
}



/*
** Implementation of random().  Return a random integer.  
*/
static void randomFunc(
  sqlite3_context *context,
  int NotUsed,
................................................................................
#ifndef SQLITE_OMIT_FLOATING_POINT
    FUNCTION(round,              1, 0, 0, roundFunc        ),
    FUNCTION(round,              2, 0, 0, roundFunc        ),
#endif
    FUNCTION(upper,              1, 0, 0, upperFunc        ),
    FUNCTION(lower,              1, 0, 0, lowerFunc        ),
    FUNCTION(coalesce,           1, 0, 0, 0                ),
    FUNCTION(coalesce,          -1, 0, 0, ifnullFunc       ),
    FUNCTION(coalesce,           0, 0, 0, 0                ),


    FUNCTION(hex,                1, 0, 0, hexFunc          ),
    FUNCTION(ifnull,             2, 0, 1, ifnullFunc       ),

    FUNCTION(random,             0, 0, 0, randomFunc       ),
    FUNCTION(randomblob,         1, 0, 0, randomBlob       ),
    FUNCTION(nullif,             2, 0, 1, nullifFunc       ),
    FUNCTION(sqlite_version,     0, 0, 0, versionFunc      ),
    FUNCTION(sqlite_source_id,   0, 0, 0, sourceidFunc     ),
    FUNCTION(quote,              1, 0, 0, quoteFunc        ),
    FUNCTION(last_insert_rowid,  0, 0, 0, last_insert_rowid),







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        z1[i] = sqlite3Tolower(z1[i]);
      }
      sqlite3_result_text(context, (char *)z1, -1, sqlite3_free);
    }
  }
}


#if 0  /* This function is never used. */
/*
** The COALESCE() and IFNULL() functions used to be implemented as shown
** here.  But now they are implemented as VDBE code so that unused arguments
** do not have to be computed.  This legacy implementation is retained as
** comment.
*/
/*
** Implementation of the IFNULL(), NVL(), and COALESCE() functions.  
** All three do the same thing.  They return the first non-NULL
** argument.
*/
static void ifnullFunc(
  sqlite3_context *context,
................................................................................
  for(i=0; i<argc; i++){
    if( SQLITE_NULL!=sqlite3_value_type(argv[i]) ){
      sqlite3_result_value(context, argv[i]);
      break;
    }
  }
}
#endif /* NOT USED */
#define ifnullFunc versionFunc   /* Substitute function - never called */

/*
** Implementation of random().  Return a random integer.  
*/
static void randomFunc(
  sqlite3_context *context,
  int NotUsed,
................................................................................
#ifndef SQLITE_OMIT_FLOATING_POINT
    FUNCTION(round,              1, 0, 0, roundFunc        ),
    FUNCTION(round,              2, 0, 0, roundFunc        ),
#endif
    FUNCTION(upper,              1, 0, 0, upperFunc        ),
    FUNCTION(lower,              1, 0, 0, lowerFunc        ),
    FUNCTION(coalesce,           1, 0, 0, 0                ),

    FUNCTION(coalesce,           0, 0, 0, 0                ),
/*  FUNCTION(coalesce,          -1, 0, 0, ifnullFunc       ), */
    {-1,SQLITE_UTF8,SQLITE_FUNC_COALESCE,0,0,ifnullFunc,0,0,"coalesce",0},
    FUNCTION(hex,                1, 0, 0, hexFunc          ),
/*  FUNCTION(ifnull,             2, 0, 0, ifnullFunc       ), */
    {2,SQLITE_UTF8,SQLITE_FUNC_COALESCE,0,0,ifnullFunc,0,0,"ifnull",0},
    FUNCTION(random,             0, 0, 0, randomFunc       ),
    FUNCTION(randomblob,         1, 0, 0, randomBlob       ),
    FUNCTION(nullif,             2, 0, 1, nullifFunc       ),
    FUNCTION(sqlite_version,     0, 0, 0, versionFunc      ),
    FUNCTION(sqlite_source_id,   0, 0, 0, sourceidFunc     ),
    FUNCTION(quote,              1, 0, 0, quoteFunc        ),
    FUNCTION(last_insert_rowid,  0, 0, 0, last_insert_rowid),

Changes to src/sqliteInt.h.

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*/
#define SQLITE_FUNC_LIKE     0x01 /* Candidate for the LIKE optimization */
#define SQLITE_FUNC_CASE     0x02 /* Case-sensitive LIKE-type function */
#define SQLITE_FUNC_EPHEM    0x04 /* Ephemeral.  Delete with VDBE */
#define SQLITE_FUNC_NEEDCOLL 0x08 /* sqlite3GetFuncCollSeq() might be called */
#define SQLITE_FUNC_PRIVATE  0x10 /* Allowed for internal use only */
#define SQLITE_FUNC_COUNT    0x20 /* Built-in count(*) aggregate */


/*
** The following three macros, FUNCTION(), LIKEFUNC() and AGGREGATE() are
** used to create the initializers for the FuncDef structures.
**
**   FUNCTION(zName, nArg, iArg, bNC, xFunc)
**     Used to create a scalar function definition of a function zName 







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*/
#define SQLITE_FUNC_LIKE     0x01 /* Candidate for the LIKE optimization */
#define SQLITE_FUNC_CASE     0x02 /* Case-sensitive LIKE-type function */
#define SQLITE_FUNC_EPHEM    0x04 /* Ephemeral.  Delete with VDBE */
#define SQLITE_FUNC_NEEDCOLL 0x08 /* sqlite3GetFuncCollSeq() might be called */
#define SQLITE_FUNC_PRIVATE  0x10 /* Allowed for internal use only */
#define SQLITE_FUNC_COUNT    0x20 /* Built-in count(*) aggregate */
#define SQLITE_FUNC_COALESCE 0x40 /* Built-in coalesce() or ifnull() function */

/*
** The following three macros, FUNCTION(), LIKEFUNC() and AGGREGATE() are
** used to create the initializers for the FuncDef structures.
**
**   FUNCTION(zName, nArg, iArg, bNC, xFunc)
**     Used to create a scalar function definition of a function zName