SQLite

  for(i=0, pC=pAggInfo->aCol; i<pAggInfo->nAccumulator; i++, pC++){
    sqlite3ExprCode(pParse, pC->pExpr, pC->iMem);
  }
  pAggInfo->directMode = 0;
  sqlite3ExprCacheClear(pParse);
}

/*
** Add a single OP_Explain instruction to the VDBE to explain a simple
** count(*) query ("SELECT count(*) FROM pTab").
*/
#ifndef SQLITE_OMIT_EXPLAIN
static void explainSimpleCount(
  Parse *pParse,                  /* Parse context */
  Table *pTab,                    /* Table being queried */
  Index *pIdx                     /* Index used to optimize scan, or NULL */
){
  if( pParse->explain==2 ){
    char *zEqp = sqlite3MPrintf(pParse->db, "SCAN TABLE %s %s%s(~%d rows)",
        pTab->zName, 
        pIdx ? "USING COVERING INDEX " : "",
        pIdx ? pIdx->zName : "",
        pTab->nRowEst
    );
    sqlite3VdbeAddOp4(
        pParse->pVdbe, OP_Explain, pParse->iSelectId, 0, 0, zEqp, P4_DYNAMIC
    );
  }
}
#else
# define explainSimpleCount(a,b,c)
#endif

/*
** Generate code for the SELECT statement given in the p argument.  
**
** The results are distributed in various ways depending on the
** contents of the SelectDest structure pointed to by argument pDest
** as follows:
**

        /* Open a read-only cursor, execute the OP_Count, close the cursor. */
        sqlite3VdbeAddOp3(v, OP_OpenRead, iCsr, iRoot, iDb);
        if( pKeyInfo ){
          sqlite3VdbeChangeP4(v, -1, (char *)pKeyInfo, P4_KEYINFO_HANDOFF);
        }
        sqlite3VdbeAddOp2(v, OP_Count, iCsr, sAggInfo.aFunc[0].iMem);
        sqlite3VdbeAddOp1(v, OP_Close, iCsr);
        explainSimpleCount(pParse, pTab, pBest);
      }else
#endif /* SQLITE_OMIT_BTREECOUNT */
      {
        /* Check if the query is of one of the following forms:
        **
        **   SELECT min(x) FROM ...
        **   SELECT max(x) FROM ...

#-------------------------------------------------------------------------
#
# eqp-1.*:        Assorted tests.
# eqp-2.*:        Tests for single select statements.
# eqp-3.*:        Select statements that execute sub-selects.
# eqp-4.*:        Compound select statements.
# ...
# eqp-7.*:        "SELECT count(*) FROM tbl" statements (VDBE code OP_Count).
#

proc det {args} { uplevel do_eqp_test $args }

do_execsql_test 1.1 {
  CREATE TABLE t1(a, b);
  CREATE INDEX i1 ON t1(a);

  }
  sqlite3 db test.db
  explain_query_plan db {%SQL%}
  db close
  exit
}

# Do a "Print Explain Query Plan" test.
proc do_peqp_test {tn sql res} {
  set fd [open script.tcl w]
  puts $fd [string map [list %SQL% $sql] $::boilerplate]
  close $fd

  uplevel do_test $tn [list {
    set fd [open "|[info nameofexec] script.tcl"]

} [string trimleft {
1 0 0 SCAN TABLE t1 USING COVERING INDEX i2 (~1000000 rows)
2 0 0 SCAN TABLE t2 (~1000000 rows)
2 0 0 USE TEMP B-TREE FOR ORDER BY
0 0 0 COMPOUND SUBQUERIES 1 AND 2 (EXCEPT)
}]

#-------------------------------------------------------------------------
# The following tests - eqp-7.* - test that queries that use the OP_Count
# optimization return something sensible with EQP.

#
drop_all_tables

do_execsql_test 7.0 {
  CREATE TABLE t1(a, b);
  CREATE TABLE t2(a, b);
  CREATE INDEX i1 ON t2(a);
}

det 7.1 "SELECT count(*) FROM t1" {
  0 0 0 {SCAN TABLE t1 (~1000000 rows)}
}

det 7.2 "SELECT count(*) FROM t2" {
  0 0 0 {SCAN TABLE t2 USING COVERING INDEX i1(~1000000 rows)}
}

do_execsql_test 7.3 {
  INSERT INTO t1 VALUES(1, 2);
  INSERT INTO t1 VALUES(3, 4);

  INSERT INTO t2 VALUES(1, 2);
  INSERT INTO t2 VALUES(3, 4);
  INSERT INTO t2 VALUES(5, 6);
 
  ANALYZE;
}

db close
sqlite3 db test.db

det 7.4 "SELECT count(*) FROM t1" {
  0 0 0 {SCAN TABLE t1 (~2 rows)}
}

det 7.5 "SELECT count(*) FROM t2" {
  0 0 0 {SCAN TABLE t2 USING COVERING INDEX i1(~3 rows)}
}


finish_test