Index: src/window.c ================================================================== --- src/window.c +++ src/window.c @@ -1497,23 +1497,82 @@ } } typedef struct WindowCodeArg WindowCodeArg; typedef struct WindowCsrAndReg WindowCsrAndReg; + +/* +** See comments above struct WindowCodeArg. +*/ struct WindowCsrAndReg { - int csr; - int reg; + int csr; /* Cursor number */ + int reg; /* First in array of peer values */ }; +/* +** A single instance of this structure is allocated on the stack by +** sqlite3WindowCodeStep() and a pointer to it passed to the various helper +** routines. This is to reduce the number of arguments required by each +** helper function. +** +** regArg: +** Each window function requires an accumulator register (just as an +** ordinary aggregate function does). This variable is set to the first +** in an array of accumulator registers - one for each window function +** in the WindowCodeArg.pMWin list. +** +** eDelete: +** The window functions implementation sometimes caches the input rows +** that it processes in a temporary table. If it is not zero, this +** variable indicates when rows may be removed from the temp table (in +** order to reduce memory requirements - it would always be safe just +** to leave them there). Possible values for eDelete are: +** +** WINDOW_RETURN_ROW: +** An input row can be discarded after it is returned to the caller. +** +** WINDOW_AGGINVERSE: +** An input row can be discarded after the window functions xInverse() +** callbacks have been invoked in it. +** +** WINDOW_AGGSTEP: +** An input row can be discarded after the window functions xStep() +** callbacks have been invoked in it. +** +** start,current,end +** Consider a window-frame similar to the following: +** +** (ORDER BY a, b GROUPS BETWEEN 2 PRECEDING AND 2 FOLLOWING) +** +** The windows functions implmentation caches the input rows in a temp +** table, sorted by "a, b" (it actually populates the cache lazily, and +** aggressively removes rows once they are no longer required, but that's +** a mere detail). It keeps three cursors open on the temp table. One +** (current) that points to the next row to return to the query engine +** once its window function values have been calculated. Another (end) +** points to the next row to call the xStep() method of each window function +** on (so that it is 2 groups ahead of current). And a third (start) that +** points to the next row to call the xInverse() method of each window +** function on. +** +** Each cursor (start, current and end) consists of a VDBE cursor +** (WindowCsrAndReg.csr) and an array of registers (starting at +** WindowCodeArg.reg) that always contains a copy of the peer values +** read from the corresponding cursor. +** +** Depending on the window-frame in question, all three cursors may not +** be required. In this case both WindowCodeArg.csr and reg are set to +** 0. +*/ struct WindowCodeArg { - Parse *pParse; - Window *pMWin; - Vdbe *pVdbe; - int regGosub; - int addrGosub; - int regArg; - int eDelete; + Parse *pParse; /* Parse context */ + Window *pMWin; /* First in list of functions being processed */ + Vdbe *pVdbe; /* VDBE object */ + int addrGosub; /* OP_Gosub to this address to return one row */ + int regGosub; /* Register used with OP_Gosub(addrGosub) */ + int regArg; /* First in array of accumulator registers */ + int eDelete; /* See above */ WindowCsrAndReg start; WindowCsrAndReg current; WindowCsrAndReg end; }; @@ -1874,22 +1933,22 @@ ** a numeric type (real or integer), then the result of the addition addition ** or subtraction is a a copy of csr1.peerVal. */ static void windowCodeRangeTest( WindowCodeArg *p, - int op, /* OP_Ge, OP_Gt, or OP_Le */ - int csr1, /* Cursor number for cursor 1 */ - int regVal, /* Register containing non-negative number */ - int csr2, /* Cursor number for cursor 2 */ - int lbl /* Jump destination if the condition is true */ + int op, /* OP_Ge, OP_Gt, or OP_Le */ + int csr1, /* Cursor number for cursor 1 */ + int regVal, /* Register containing non-negative number */ + int csr2, /* Cursor number for cursor 2 */ + int lbl /* Jump destination if condition is true */ ){ Parse *pParse = p->pParse; Vdbe *v = sqlite3GetVdbe(pParse); - ExprList *pOrderBy = p->pMWin->pOrderBy; /* ORDER BY clause for this window */ - int reg1 = sqlite3GetTempReg(pParse); /* Register for csr1.peerVal+regVal */ - int reg2 = sqlite3GetTempReg(pParse); /* Regiser for csr2.peerVal */ - int regString = ++pParse->nMem; /* Register for constant value '' */ + ExprList *pOrderBy = p->pMWin->pOrderBy; /* ORDER BY clause for window */ + int reg1 = sqlite3GetTempReg(pParse); /* Reg. for csr1.peerVal+regVal */ + int reg2 = sqlite3GetTempReg(pParse); /* Reg. for csr2.peerVal */ + int regString = ++pParse->nMem; /* Reg. for constant value '' */ int arith = OP_Add; /* OP_Add or OP_Subtract */ int addrGe; /* Jump destination */ assert( op==OP_Ge || op==OP_Gt || op==OP_Le ); assert( pOrderBy && pOrderBy->nExpr==1 );