SQLite

/*
** Return the collating function associated with a function.
*/
static CollSeq *sqlite3GetFuncCollSeq(sqlite3_context *context){
  return context->pColl;
}

/*
** Indicate that the accumulator load should be skipped on this
** iteration of the aggregate loop.
*/
static void sqlite3SkipAccumulatorLoad(sqlite3_context *context){
  context->skipFlag = 1;
}

/*
** Implementation of the non-aggregate min() and max() functions
*/
static void minmaxFunc(
  sqlite3_context *context,
  int argc,

  int NotUsed, 
  sqlite3_value **argv
){
  Mem *pArg  = (Mem *)argv[0];
  Mem *pBest;
  UNUSED_PARAMETER(NotUsed);


  pBest = (Mem *)sqlite3_aggregate_context(context, sizeof(*pBest));
  if( !pBest ) return;

  if( sqlite3_value_type(argv[0])==SQLITE_NULL ){
    if( pBest->flags ) sqlite3SkipAccumulatorLoad(context);
  }else if( pBest->flags ){
    int max;
    int cmp;
    CollSeq *pColl = sqlite3GetFuncCollSeq(context);
    /* This step function is used for both the min() and max() aggregates,
    ** the only difference between the two being that the sense of the
    ** comparison is inverted. For the max() aggregate, the
    ** sqlite3_user_data() function returns (void *)-1. For min() it
    ** returns (void *)db, where db is the sqlite3* database pointer.
    ** Therefore the next statement sets variable 'max' to 1 for the max()
    ** aggregate, or 0 for min().
    */
    max = sqlite3_user_data(context)!=0;
    cmp = sqlite3MemCompare(pBest, pArg, pColl);
    if( (max && cmp<0) || (!max && cmp>0) ){
      sqlite3VdbeMemCopy(pBest, pArg);
    }else{
      sqlite3SkipAccumulatorLoad(context);
    }
  }else{
    sqlite3VdbeMemCopy(pBest, pArg);
  }
}
static void minMaxFinalize(sqlite3_context *context){
  sqlite3_value *pRes;
  pRes = (sqlite3_value *)sqlite3_aggregate_context(context, 0);
  if( pRes ){
    if( pRes->flags ){
      sqlite3_result_value(context, pRes);
    }
    sqlite3VdbeMemRelease(pRes);
  }
}

/*

/*
** Update the accumulator memory cells for an aggregate based on
** the current cursor position.
*/
static void updateAccumulator(Parse *pParse, AggInfo *pAggInfo){
  Vdbe *v = pParse->pVdbe;
  int i;
  int regHit = 0;
  int addrHitTest = 0;
  struct AggInfo_func *pF;
  struct AggInfo_col *pC;

  pAggInfo->directMode = 1;
  sqlite3ExprCacheClear(pParse);
  for(i=0, pF=pAggInfo->aFunc; i<pAggInfo->nFunc; i++, pF++){
    int nArg;

      assert( pList!=0 );  /* pList!=0 if pF->pFunc has NEEDCOLL */
      for(j=0, pItem=pList->a; !pColl && j<nArg; j++, pItem++){
        pColl = sqlite3ExprCollSeq(pParse, pItem->pExpr);
      }
      if( !pColl ){
        pColl = pParse->db->pDfltColl;
      }
      if( regHit==0 && pAggInfo->nAccumulator ) regHit = ++pParse->nMem;
      sqlite3VdbeAddOp4(v, OP_CollSeq, regHit, 0, 0, (char *)pColl, P4_COLLSEQ);
    }
    sqlite3VdbeAddOp4(v, OP_AggStep, 0, regAgg, pF->iMem,
                      (void*)pF->pFunc, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, (u8)nArg);
    sqlite3ExprCacheAffinityChange(pParse, regAgg, nArg);
    sqlite3ReleaseTempRange(pParse, regAgg, nArg);
    if( addrNext ){

  ** to pC->iMem. But by the time the value is used, the original register
  ** may have been used, invalidating the underlying buffer holding the
  ** text or blob value. See ticket [883034dcb5].
  **
  ** Another solution would be to change the OP_SCopy used to copy cached
  ** values to an OP_Copy.
  */
  if( regHit ){
    addrHitTest = sqlite3VdbeAddOp1(v, OP_If, regHit);
  }
  sqlite3ExprCacheClear(pParse);
  for(i=0, pC=pAggInfo->aCol; i<pAggInfo->nAccumulator; i++, pC++){
    sqlite3ExprCode(pParse, pC->pExpr, pC->iMem);
  }
  pAggInfo->directMode = 0;
  sqlite3ExprCacheClear(pParse);
  if( addrHitTest ){
    sqlite3VdbeJumpHere(v, addrHitTest);
  }
}

/*
** Add a single OP_Explain instruction to the VDBE to explain a simple
** count(*) query ("SELECT count(*) FROM pTab").
*/
#ifndef SQLITE_OMIT_EXPLAIN

  break;

arithmetic_result_is_null:
  sqlite3VdbeMemSetNull(pOut);
  break;
}

/* Opcode: CollSeq P1 * * P4
**
** P4 is a pointer to a CollSeq struct. If the next call to a user function
** or aggregate calls sqlite3GetFuncCollSeq(), this collation sequence will
** be returned. This is used by the built-in min(), max() and nullif()
** functions.
**
** If P1 is not zero, then it is a register that a subsequent min() or
** max() aggregate will set to 1 if the current row is not the minimum or
** maximum.  The P1 register is initialized to 0 by this instruction.
**
** The interface used by the implementation of the aforementioned functions
** to retrieve the collation sequence set by this opcode is not available
** publicly, only to user functions defined in func.c.
*/
case OP_CollSeq: {
  assert( pOp->p4type==P4_COLLSEQ );
  if( pOp->p1 ){
    sqlite3VdbeMemSetInt64(&aMem[pOp->p1], 0);
  }
  break;
}

/* Opcode: Function P1 P2 P3 P4 P5
**
** Invoke a user function (P4 is a pointer to a Function structure that
** defines the function) with P5 arguments taken from register P2 and

  ctx.s.flags = MEM_Null;
  ctx.s.z = 0;
  ctx.s.zMalloc = 0;
  ctx.s.xDel = 0;
  ctx.s.db = db;
  ctx.isError = 0;
  ctx.pColl = 0;
  ctx.skipFlag = 0;
  if( ctx.pFunc->flags & SQLITE_FUNC_NEEDCOLL ){
    assert( pOp>p->aOp );
    assert( pOp[-1].p4type==P4_COLLSEQ );
    assert( pOp[-1].opcode==OP_CollSeq );
    ctx.pColl = pOp[-1].p4.pColl;
  }
  (ctx.pFunc->xStep)(&ctx, n, apVal); /* IMP: R-24505-23230 */
  if( ctx.isError ){
    sqlite3SetString(&p->zErrMsg, db, "%s", sqlite3_value_text(&ctx.s));
    rc = ctx.isError;
  }
  if( ctx.skipFlag ){
    assert( pOp[-1].opcode==OP_CollSeq );
    i = pOp[-1].p1;
    if( i ) sqlite3VdbeMemSetInt64(&aMem[i], 1);
  }

  sqlite3VdbeMemRelease(&ctx.s);

  break;
}

/* Opcode: AggFinal P1 P2 * P4 *

struct sqlite3_context {
  FuncDef *pFunc;       /* Pointer to function information.  MUST BE FIRST */
  VdbeFunc *pVdbeFunc;  /* Auxilary data, if created. */
  Mem s;                /* The return value is stored here */
  Mem *pMem;            /* Memory cell used to store aggregate context */
  int isError;          /* Error code returned by the function. */
  CollSeq *pColl;       /* Collating sequence */
  int skipFlag;         /* Skip skip accumulator loading if true */
};

/*
** An Explain object accumulates indented output which is helpful
** in describing recursive data structures.
*/
struct Explain {

  2  "SELECT * FROM z1,z2 LIMIT 1"          {51.65 -59.58 belfries {} 21}
  3  "SELECT z1.* FROM z1,z2 LIMIT 1"       {51.65 -59.58 belfries}
  4  "SELECT z2.* FROM z1,z2 LIMIT 1"       {{} 21}
  5  "SELECT z2.*, z1.* FROM z1,z2 LIMIT 1" {{} 21 51.65 -59.58 belfries}

  6  "SELECT count(*), * FROM z1"           {6 63 born -26}
  7  "SELECT max(a), * FROM z1"             {63 63 born -26}
  8  "SELECT *, min(a) FROM z1"             {-5 {} 75 -5}

  9  "SELECT *,* FROM z1,z2 LIMIT 1" {        
     51.65 -59.58 belfries {} 21 51.65 -59.58 belfries {} 21
  }
  10 "SELECT z1.*,z1.* FROM z2,z1 LIMIT 1" {        
     51.65 -59.58 belfries 51.65 -59.58 belfries
  }

# 2012 February 02
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
# Test for queries of the form:  
#
#    SELECT p, max(q) FROM t1;
#
# Demonstration that the value returned for p is on the same row as 
# the maximum q.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

do_test minmax4-1.1 {
  db eval {
    CREATE TABLE t1(p,q);
    SELECT p, max(q) FROM t1;
  }
} {{} {}}
do_test minmax4-1.2 {
  db eval {
    SELECT p, min(q) FROM t1;
  }
} {{} {}}
do_test minmax4-1.3 {
  db eval {
    INSERT INTO t1 VALUES(1,2);
    SELECT p, max(q) FROM t1;
  }
} {1 2}
do_test minmax4-1.4 {
  db eval {
    SELECT p, min(q) FROM t1;
  }
} {1 2}
do_test minmax4-1.5 {
  db eval {
    INSERT INTO t1 VALUES(3,4);
    SELECT p, max(q) FROM t1;
  }
} {3 4}
do_test minmax4-1.6 {
  db eval {
    SELECT p, min(q) FROM t1;
  }
} {1 2}
do_test minmax4-1.7 {
  db eval {
    INSERT INTO t1 VALUES(5,0);
    SELECT p, max(q) FROM t1;
  }
} {3 4}
do_test minmax4-1.8 {
  db eval {
    SELECT p, min(q) FROM t1;
  }
} {5 0}
do_test minmax4-1.9 {
  db eval {
    INSERT INTO t1 VALUES(6,1);
    SELECT p, max(q) FROM t1;
  }
} {3 4}
do_test minmax4-1.10 {
  db eval {
    SELECT p, min(q) FROM t1;
  }
} {5 0}
do_test minmax4-1.11 {
  db eval {
    INSERT INTO t1 VALUES(7,NULL);
    SELECT p, max(q) FROM t1;
  }
} {3 4}
do_test minmax4-1.12 {
  db eval {
    SELECT p, min(q) FROM t1;
  }
} {5 0}
do_test minmax4-1.13 {
  db eval {
    DELETE FROM t1 WHERE q IS NOT NULL;
    SELECT p, max(q) FROM t1;
  }
} {7 {}}
do_test minmax4-1.14 {
  db eval {
    SELECT p, min(q) FROM t1;
  }
} {7 {}}

do_test minmax4-2.1 {
  db eval {
    CREATE TABLE t2(a,b,c);
    INSERT INTO t2 VALUES
         (1,null,2),
         (1,2,3),
         (1,1,4),
         (2,3,5);
    SELECT a, max(b), c FROM t2 GROUP BY a ORDER BY a;
  }
} {1 2 3 2 3 5}
do_test minmax4-2.2 {
  db eval {
    SELECT a, min(b), c FROM t2 GROUP BY a ORDER BY a;
  }
} {1 1 4 2 3 5}
do_test minmax4-2.3 {
  db eval {
    SELECT a, min(b), avg(b), count(b), c FROM t2 GROUP BY a ORDER BY a DESC;
  }
} {2 3 3.0 1 5 1 1 1.5 2 4}
do_test minmax4-2.4 {
  db eval {
    SELECT a, min(b), max(b), c FROM t2 GROUP BY a ORDER BY a;
  }
} {1 1 2 3 2 3 3 5}
do_test minmax4-2.5 {
  db eval {
    SELECT a, max(b), min(b), c FROM t2 GROUP BY a ORDER BY a;
  }
} {1 2 1 4 2 3 3 5}
do_test minmax4-2.6 {
  db eval {
    SELECT a, max(b), b, max(c), c FROM t2 GROUP BY a ORDER BY a;
  }
} {1 2 1 4 4 2 3 3 5 5}
do_test minmax4-2.7 {
  db eval {
    SELECT a, min(b), b, min(c), c FROM t2 GROUP BY a ORDER BY a;
  }
} {1 1 {} 2 2 2 3 3 5 5}



finish_test