Postgresql动态执行EXECUTING语法解析过程

背景

Postgresql中PLPGSQL支持动态拼接SQL并执行：
https://www.postgresql.org/docs/current/plpgsql-statements.html#PLPGSQL-STATEMENTS-EXECUTING-DYN
例如：

EXECUTE 'SELECT count(*) FROM mytable WHERE inserted_by = $1 AND inserted <= $2'INTO cUSING checked_user, checked_date;

本篇简单分析下EXECUTE执行流程。

测试case

drop table u1tbl;
create table u1tbl(i int);
insert into u1tbl values (1);
insert into u1tbl values (2);
insert into u1tbl values (3);drop function f1();
CREATE OR REPLACE FUNCTION f1() RETURNS int AS $$
DECLAREid int;i1 int := 1;i2 int := 2;
BEGINEXECUTE 'SELECT sum(i) FROM u1tbl WHERE i >= $1 AND i <= $2'INTO idUSING i1, i2; return id;
END;
$$ LANGUAGE plpgsql;select f1();postgres=# select f1();f1
----3
(1 row)

EXECUTE解析流程

EXECUTE 'SELECT sum(i) FROM u1tbl WHERE i >= $1 AND i <= $2' INTO id USING i1, i2;

1、第一次read_sql_construct中会调用多次lex把需要的SQL全部提取出来，实际情况是第一次lex后，会把EXECUTE后''内的所有文本拿出来，给出一个SCONST的token。

过程如下：

EXECUTE 'SELECT sum(i) FROM u1tbl WHERE i >= $1 AND i <= $2' INTO id USING i1, i2; |---------------     SCONST     -----------------|  K_INTO  K_USING[pl_gram.y]     stmt_dynexecute : K_EXECUTE      read_sql_construct
[   scan.l]     {xqstart}                        BEGIN(xq);
[   scan.l]     <xq,xus>{xqinside}               addlit(yytext, yyleng, yyscanner);
[   scan.l]     <xb,xh,xq,xe,xus>{quote}         BEGIN(xqs);
[   scan.l]     <xqs><<EOF>>                     BEGIN(INITIAL);  return SCONST;
[pl_gram.y]

2、后面在循环体里面的read_sql_construct会把USING后面的所有SQL或变量名读取出来，按,分隔。每一个SQL或变量记为一个expr作为链表挂在PLpgSQL_stmt_dynexecute->param后。

最后返回的PLpgSQL_stmt_dynexecute结构：

{cmd_type = PLPGSQL_STMT_DYNEXECUTE, lineno = 7, stmtid = 1, query = 0x1a3a328, <PLpgSQL_expr> 'SELECT sum(i) FROM u1tbl WHERE i >= $1 AND i <= $2'into = true, strict = false, target = 0x1a3a490, <PLpgSQL_variable> dno=4 --> ((PLpgSQL_row*)plpgsql_Datums[4])params = 0x1a3a600  List: <PLpgSQL_expr> <PLpgSQL_expr>
}

pl_gram.y相关源码

stmt_dynexecute : K_EXECUTE{PLpgSQL_stmt_dynexecute *new;PLpgSQL_expr *expr;int endtoken;expr = read_sql_construct(K_INTO, K_USING, ';',"INTO or USING or ;",RAW_PARSE_PLPGSQL_EXPR,true, true, true,NULL, &endtoken);new = palloc(sizeof(PLpgSQL_stmt_dynexecute));new->cmd_type = PLPGSQL_STMT_DYNEXECUTE;new->lineno = plpgsql_location_to_lineno(@1);new->stmtid = ++plpgsql_curr_compile->nstatements;new->query = expr;new->into = false;new->strict = false;new->target = NULL;new->params = NIL;/** We loop to allow the INTO and USING clauses to* appear in either order, since people easily get* that wrong.  This coding also prevents "INTO foo"* from getting absorbed into a USING expression,* which is *really* confusing.*/for (;;){if (endtoken == K_INTO){if (new->into)         /* multiple INTO */yyerror("syntax error");new->into = true;read_into_target(&new->target, &new->strict);endtoken = yylex();}else if (endtoken == K_USING){if (new->params)       /* multiple USING */yyerror("syntax error");do{expr = read_sql_construct(',', ';', K_INTO,", or ; or INTO",RAW_PARSE_PLPGSQL_EXPR,true, true, true,NULL, &endtoken);new->params = lappend(new->params, expr);} while (endtoken == ',');}else if (endtoken == ';')break;elseyyerror("syntax error");}$$ = (PLpgSQL_stmt *)new;};

SELECT sum(i) FROM u1tbl WHERE i >= $1 AND i <= $2’