PostgreSQL 源码解读（202）- 查询#115(类型转换)

2025-04-14 技术教程

本节简单介绍了PostgreSQL中的类型转换实现.
首先来看看几个示例SQL:

testdb=# testdb=# drop table if exists t_conv;om t_conv where id = '1'::text;explain verbose select * from t_conv where id > '13'::text;DROP TABLEtestdb=# create table t_conv(id int);CREATE TABLEtestdb=# testdb=# insert into t_conv values(1);INSERT 0 1testdb=# insert into t_conv values(2);INSERT 0 1testdb=#

查询条件为id = ‘1’,’1’转换为int进行比较.

testdb=# explain verbose select * from t_conv where id = '1'; QUERY PLAN --------------------------------------------------------------- Seq Scan on public.t_conv (cost=0.00..41.88 rows=13 width=4) Output: id Filter: (t_conv.id = 1)(3 rows)

查询条件为id = ‘1.1’,出错(1.1无法转换为整型)

testdb=# explain verbose select * from t_conv where id = '1.1';psql: ERROR: invalid input syntax for type integer: "1.1"LINE 1: explain verbose select * from t_conv where id = '1.1'; ^

查询条件为id = ‘1’::text,出错(text和int4没有转换规则)

testdb=# explain verbose select * from t_conv where id = '1'::text;psql: ERROR: operator does not exist: integer = textLINE 1: explain verbose select * from t_conv where id = '1'::text; ^HINT: No operator matches the given name and argument types. You might need to add explicit type casts.testdb=#

查询条件为id > ‘13’::text,转换为numeric进行比较

testdb=# explain verbose select * from t_conv where id > '13'::text; QUERY PLAN ---------------------------------------------------------------- Seq Scan on public.t_conv (cost=0.00..48.25 rows=850 width=4) Output: id Filter: ((t_conv.id)::numeric > '13'::numeric)(3 rows)testdb=#

系统转换规则定义,”>”操作符有定义text&int的比较,而”=”操作符没有定义,因此”select * from t_conv where id = ‘1’::text”语句会出错.

总结一下:
解析表达式,涉及不同数据类型时:
1.如有相应类型的Operator定义(pg_operator),则尝试进行类型转换,否则报错;
2.如有相应类型的转换规则,转换为目标类型后解析,否则报错.

一、数据结构

Form_pg_operator
pg_operator中的定义,代码会其中的定义转换为FormData_pg_operator结构体

/* ---------------- * pg_operator definition. cpp turns this into * typedef struct FormData_pg_operator * ---------------- */CATALOG(pg_operator,2617,OperatorRelationId){ Oid oid; /* oid */ /* name of operator */ NameData oprname; /* OID of namespace containing this oper */ Oid oprnamespace BKI_DEFAULT(PGNSP); /* operator owner */ Oid oprowner BKI_DEFAULT(PGUID); /* 'l', 'r', or 'b' */ char oprkind BKI_DEFAULT(b); /* can be used in merge join? */ bool oprcanmerge BKI_DEFAULT(f); /* can be used in hash join? */ bool oprcanhash BKI_DEFAULT(f); /* left arg type, or 0 if 'l' oprkind */ Oid oprleft BKI_LOOKUP(pg_type); /* right arg type, or 0 if 'r' oprkind */ Oid oprright BKI_LOOKUP(pg_type); /* result datatype */ Oid oprresult BKI_LOOKUP(pg_type); /* OID of commutator oper, or 0 if none */ Oid oprcom BKI_DEFAULT(0) BKI_LOOKUP(pg_operator); /* OID of negator oper, or 0 if none */ Oid oprnegate BKI_DEFAULT(0) BKI_LOOKUP(pg_operator); /* OID of underlying function */ regproc oprcode BKI_LOOKUP(pg_proc); /* OID of restriction estimator, or 0 */ regproc oprrest BKI_DEFAULT(-) BKI_LOOKUP(pg_proc); /* OID of join estimator, or 0 */ regproc oprjoin BKI_DEFAULT(-) BKI_LOOKUP(pg_proc);} FormData_pg_operator;/* ---------------- * Form_pg_operator corresponds to a pointer to a tuple with * the format of pg_operator relation. * ---------------- */typedef FormData_pg_operator *Form_pg_operator;二、源码解读

make_op
变换操作符表达式以确保类型兼容,会存在某些类型转换.

/* * make_op() * Operator expression construction. * * Transform operator expression ensuring type compatibility. * This is where some type conversion happens. * 变换操作符表达式以确保类型兼容,会存在某些类型转换. * * last_srf should be a copy of pstate->p_last_srf from just before we * started transforming the operator's arguments; this is used for nested-SRF * detection. If the caller will throw an error anyway for a set-returning * expression, it's okay to cheat and just pass pstate->p_last_srf. * last_srf应为pstate->p_last_srf的一个拷贝. */Expr *make_op(ParseState *pstate, List *opname, Node *ltree, Node *rtree, Node *last_srf, int location){ Oid ltypeId,//左算子类型OID rtypeId;//右算子类型OID Operator tup;//操作符tuple Form_pg_operator opform;//操作符form(参照pg_operator) Oid actual_arg_types[2];//实际参数类型 Oid declared_arg_types[2];//操作符声明的参数类型 int nargs;//参数格式 List *args;//参数链表 Oid rettype;//返回结果类型 OpExpr *result;//结果 /* Select the operator */ //选择操作符 if (rtree == NULL) { /* right operator */ //右树为NULL,则为右操作符,如阶乘运算符"!" : 10! ltypeId = exprType(ltree); rtypeId = InvalidOid; tup = right_oper(pstate, opname, ltypeId, false, location); } else if (ltree == NULL) { /* left operator */ //左树为空,则为左操作符,如按位NOT运算符 : "~21" rtypeId = exprType(rtree); ltypeId = InvalidOid; tup = left_oper(pstate, opname, rtypeId, false, location); } else { /* otherwise, binary operator */ //二元操作符 ltypeId = exprType(ltree); rtypeId = exprType(rtree); tup = oper(pstate, opname, ltypeId, rtypeId, false, location); } //获取操作符 opform = (Form_pg_operator) GETSTRUCT(tup); /* Check it's not a shell */ if (!RegProcedureIsValid(opform->oprcode)) ereport(ERROR, (errcode(ERRCODE_UNDEFINED_FUNCTION), errmsg("operator is only a shell: %s", op_signature_string(opname, opform->oprkind, opform->oprleft, opform->oprright)), parser_errposition(pstate, location))); /* Do typecasting and build the expression tree */ //执行类型转换并构建表达式树 if (rtree == NULL) { /* right operator */ args = list_make1(ltree);//参数 actual_arg_types[0] = ltypeId;//左实际参数类型 declared_arg_types[0] = opform->oprleft;//声明类型 nargs = 1;//参数个数 } else if (ltree == NULL) { /* left operator */ args = list_make1(rtree); actual_arg_types[0] = rtypeId; declared_arg_types[0] = opform->oprright; nargs = 1; } else { /* otherwise, binary operator */ args = list_make2(ltree, rtree); actual_arg_types[0] = ltypeId; actual_arg_types[1] = rtypeId; declared_arg_types[0] = opform->oprleft; declared_arg_types[1] = opform->oprright; nargs = 2; } /* * enforce consistency with polymorphic argument and return types, * possibly adjusting return type or declared_arg_types (which will be * used as the cast destination by make_fn_arguments) * 强制多态参数与返回类型的一致性,可能会调整返回类型或者declared_arg_types * (可能会在函数make_fn_arguments中作为转换目标类型) */ rettype = enforce_generic_type_consistency(actual_arg_types, declared_arg_types, nargs, opform->oprresult, false); /* perform the necessary typecasting of arguments */ //参数类型转换 make_fn_arguments(pstate, args, actual_arg_types, declared_arg_types); /* and build the expression node */ //构建表达式节点 result = makeNode(OpExpr); result->opno = oprid(tup); result->opfuncid = opform->oprcode; result->opresulttype = rettype; result->opretset = get_func_retset(opform->oprcode); /* opcollid and inputcollid will be set by parse_collate.c */ result->args = args; result->location = location; /* if it returns a set, check that's OK */ if (result->opretset) { check_srf_call_placement(pstate, last_srf, location); /* ... and remember it for error checks at higher levels */ pstate->p_last_srf = (Node *) result; } ReleaseSysCache(tup); return (Expr *) result;}

make_fn_arguments
给定实际的参数表达式和期望的输入类型,为表达式树执行有需要的类型转换.

/* * make_fn_arguments() * * Given the actual argument expressions for a function, and the desired * input types for the function, add any necessary typecasting to the * expression tree. Caller should already have verified that casting is * allowed. * 给定实际的参数表达式和期望的输入类型,为表达式树执行有需要的类型转换. * 调用者已验证转换是可行的. * * Caution: given argument list is modified in-place. * 就地转换参数类型. * * As with coerce_type, pstate may be NULL if no special unknown-Param * processing is wanted. */voidmake_fn_arguments(ParseState *pstate, List *fargs, Oid *actual_arg_types, Oid *declared_arg_types){ ListCell *current_fargs; int i = 0; foreach(current_fargs, fargs) { /* types don't match? then force coercion using a function call... */ //类型不匹配? if (actual_arg_types[i] != declared_arg_types[i]) { //获取节点 Node *node = (Node *) lfirst(current_fargs); /* * If arg is a NamedArgExpr, coerce its input expr instead --- we * want the NamedArgExpr to stay at the top level of the list. * 如果参数是NamedArgExpr,则强制转换为输入表达式 */ if (IsA(node, NamedArgExpr)) { NamedArgExpr *na = (NamedArgExpr *) node; node = coerce_type(pstate, (Node *) na->arg, actual_arg_types[i], declared_arg_types[i], -1, COERCION_IMPLICIT, COERCE_IMPLICIT_CAST, -1); na->arg = (Expr *) node; } else { //执行转换 node = coerce_type(pstate, node, actual_arg_types[i], declared_arg_types[i], -1, COERCION_IMPLICIT, COERCE_IMPLICIT_CAST, -1); lfirst(current_fargs) = node; } } i++; }}三、跟踪分析

SQL脚本

testdb=# select * from t_conv where id = '1';

跟踪分析

(gdb) b make_opBreakpoint 2 at 0x619cdb: file parse_oper.c, line 762.(gdb) cContinuing.Breakpoint 2, make_op (pstate=0x22d6e30, opname=0x22d6c48, ltree=0x22d7620, rtree=0x22d7678, last_srf=0x0, location=30) at parse_oper.c:762762 if (rtree == NULL)(gdb)

调用栈信息

(gdb) bt#0 make_op (pstate=0x22d6e30, opname=0x22d6c48, ltree=0x22d7620, rtree=0x22d7678, last_srf=0x0, location=30) at parse_oper.c:859#1 0x000000000060df9c in transformAExprOp (pstate=0x22d6e30, a=0x22d6ba0) at parse_expr.c:1010#2 0x000000000060c55b in transformExprRecurse (pstate=0x22d6e30, expr=0x22d6ba0) at parse_expr.c:216#3 0x000000000060c298 in transformExpr (pstate=0x22d6e30, expr=0x22d6ba0, exprKind=EXPR_KIND_WHERE) at parse_expr.c:155#4 0x0000000000602164 in transformWhereClause (pstate=0x22d6e30, clause=0x22d6ba0, exprKind=EXPR_KIND_WHERE, constructName=0xb458a7 "WHERE") at parse_clause.c:1691#5 0x00000000005c7eb5 in transformSelectStmt (pstate=0x22d6e30, stmt=0x22d6c80) at analyze.c:1239#6 0x00000000005c6392 in transformStmt (pstate=0x22d6e30, parseTree=0x22d6c80) at analyze.c:301#7 0x00000000005c626d in transformOptionalSelectInto (pstate=0x22d6e30, parseTree=0x22d6c80) at analyze.c:246#8 0x00000000005c612b in transformTopLevelStmt (pstate=0x22d6e30, parseTree=0x22d6d98) at analyze.c:196#9 0x00000000005c5f83 in parse_analyze (parseTree=0x22d6d98, sourceText=0x22d5e08 "select * from t_conv where id = '1';", paramTypes=0x0, numParams=0, queryEnv=0x0) at analyze.c:116#10 0x00000000008e78d9 in pg_analyze_and_rewrite (parsetree=0x22d6d98, query_string=0x22d5e08 "select * from t_conv where id = '1';", paramTypes=0x0, numParams=0, queryEnv=0x0) at postgres.c:695#11 0x00000000008e7f23 in exec_simple_query (query_string=0x22d5e08 "select * from t_conv where id = '1';") at postgres.c:1140#12 0x00000000008ec3a0 in PostgresMain (argc=1, argv=0x22ffdb8, dbname=0x22ffc00 "testdb", username=0x22d2a68 "pg12") at postgres.c:4249#13 0x0000000000843650 in BackendRun (port=0x22f7be0) at postmaster.c:4431#14 0x0000000000842e2e in BackendStartup (port=0x22f7be0) at postmaster.c:4122#15 0x000000000083f06a in ServerLoop () at postmaster.c:1704#16 0x000000000083e920 in PostmasterMain (argc=1, argv=0x22d0a20) at postmaster.c:1377#17 0x000000000075f834 in main (argc=1, argv=0x22d0a20) at main.c:228

输入参数
操作符为”=”;ltree为字段列,类型为int4(vartype = 23);rtree为常量,类型为unknown(consttype = 705);last_srf为NULL;该操作符在字符串中的偏移为30.

(gdb) p *pstate$7 = {parentParseState = 0x0, p_sourcetext = 0x22d5e08 "select * from t_conv where id = '1';", p_rtable = 0x22d72a0, p_joinexprs = 0x0, p_joinlist = 0x22d73a8, p_namespace = 0x22d7328, p_lateral_active = false, p_ctenamespace = 0x0, p_future_ctes = 0x0, p_parent_cte = 0x0, p_target_relation = 0x0, p_target_rangetblentry = 0x0, p_is_insert = false, p_windowdefs = 0x0, p_expr_kind = EXPR_KIND_WHERE, p_next_resno = 2, p_multiassign_exprs = 0x0, p_locking_clause = 0x0, p_locked_from_parent = false, p_resolve_unknowns = true, p_queryEnv = 0x0, p_hasAggs = false, p_hasWindowFuncs = false, p_hasTargetSRFs = false, p_hasSubLinks = false, p_hasModifyingCTE = false, p_last_srf = 0x0, p_pre_columnref_hook = 0x0, p_post_columnref_hook = 0x0, p_paramref_hook = 0x0, p_coerce_param_hook = 0x0, p_ref_hook_state = 0x0}(gdb) p *opname$8 = {type = T_List, length = 1, head = 0x22d6c20, tail = 0x22d6c20}(gdb) p *(Node *)opname->head->data.ptr_value$9 = {type = T_String}(gdb) p *(Value *)opname->head->data.ptr_value$14 = {type = T_String, val = {ival = 12298942, str = 0xbbaabe "="}}(gdb) p *ltree$15 = {type = T_Var}(gdb) p *(Var *)ltree$16 = {xpr = {type = T_Var}, varno = 1, varattno = 1, vartype = 23, vartypmod = -1, varcollid = 0, varlevelsup = 0, varnoold = 1, varoattno = 1, location = 27}(gdb) p *(Const *)rtree$18 = {xpr = {type = T_Const}, consttype = 705, consttypmod = -1, constcollid = 0, constlen = -2, constvalue = 36531016, constisnull = false, constbyval = false, location = 32} ###testdb=# select typname from pg_type where oid in (23,705); typname --------- int4 unknown(2 rows)###

确定操作符(二元操作符)

(gdb) n769 else if (ltree == NULL)(gdb) 779 ltypeId = exprType(ltree);(gdb) 780 rtypeId = exprType(rtree);(gdb) 781 tup = oper(pstate, opname, ltypeId, rtypeId, false, location);(gdb) p ltypeId$19 = 23(gdb) p rtypeId$20 = 705(gdb)

获取操作符(对应pg_operator)

(gdb) n784 opform = (Form_pg_operator) GETSTRUCT(tup);(gdb) 787 if (!RegProcedureIsValid(opform->oprcode))(gdb) p *opform$21 = {oid = 96, oprname = {data = "=", '\000' <repeats 62 times>}, oprnamespace = 11, oprowner = 10, oprkind = 98 'b', oprcanmerge = true, oprcanhash = true, oprleft = 23, oprright = 23, oprresult = 16, oprcom = 96, oprnegate = 518, oprcode = 65, oprrest = 101, oprjoin = 105}(gdb)

执行类型转换并构建表达式树.
实际类型为23&705,操作符声明操作类型为23&23

(gdb) n798 if (rtree == NULL)(gdb) 806 else if (ltree == NULL)(gdb) 817 args = list_make2(ltree, rtree);(gdb) 818 actual_arg_types[0] = ltypeId;(gdb) 819 actual_arg_types[1] = rtypeId;(gdb) 820 declared_arg_types[0] = opform->oprleft;(gdb) 821 declared_arg_types[1] = opform->oprright;(gdb) 822 nargs = 2;(gdb) p opform->oprleft$22 = 23(gdb) p opform->oprright$23 = 23(gdb) n830 rettype = enforce_generic_type_consistency(actual_arg_types,(gdb)

进入函数make_fn_arguments

(gdb) 837 make_fn_arguments(pstate, args, actual_arg_types, declared_arg_types);(gdb) nBreakpoint 1, make_fn_arguments (pstate=0x22d6e30, fargs=0x22d76f8, actual_arg_types=0x7ffda1b2af80, declared_arg_types=0x7ffda1b2af70) at parse_func.c:18351835 int i = 0;(gdb)

调用coerce_type函数执行转换,unknown -> int4

(gdb) n1837 foreach(current_fargs, fargs)(gdb) 1840 if (actual_arg_types[i] != declared_arg_types[i])(gdb) 1873 i++;(gdb) 1837 foreach(current_fargs, fargs)(gdb) 1840 if (actual_arg_types[i] != declared_arg_types[i])(gdb) p actual_arg_types[i]$24 = 705(gdb) p declared_arg_types[i]$25 = 23(gdb) n1842 Node *node = (Node *) lfirst(current_fargs);(gdb) n1848 if (IsA(node, NamedArgExpr))(gdb) 1866 declared_arg_types[i], -1,(gdb) 1863 node = coerce_type(pstate,(gdb) 1865 actual_arg_types[i],(gdb) 1863 node = coerce_type(pstate,(gdb) 1870 lfirst(current_fargs) = node;(gdb) p *node$26 = {type = T_Const}(gdb) p *(Const *)node$27 = {xpr = {type = T_Const}, consttype = 23, consttypmod = -1, constcollid = 0, constlen = 4, constvalue = 1, constisnull = false, constbyval = true, location = 32}(gdb)

完成调用

(gdb) n1873 i++;(gdb) 1837 foreach(current_fargs, fargs)(gdb) 1875 }(gdb) make_op (pstate=0x22d6e30, opname=0x22d6c48, ltree=0x22d7620, rtree=0x22d7678, last_srf=0x0, location=30) at parse_oper.c:840840 result = makeNode(OpExpr);

回到make_op,构造结果result结构体

(gdb) 841 result->opno = oprid(tup);(gdb) 842 result->opfuncid = opform->oprcode;(gdb) 843 result->opresulttype = rettype;(gdb) 844 result->opretset = get_func_retset(opform->oprcode);(gdb) 846 result->args = args;(gdb) 847 result->location = location;(gdb) 850 if (result->opretset)(gdb) 857 ReleaseSysCache(tup);(gdb) 859 return (Expr *) result;(gdb) p *(Expr *) result$28 = {type = T_OpExpr}(gdb) p *(OpExpr *) result$29 = {xpr = {type = T_OpExpr}, opno = 96, opfuncid = 65, opresulttype = 16, opretset = false, opcollid = 0, inputcollid = 0, args = 0x22d76f8, location = 30}(gdb)

DONE!

实现函数coerce_type下节再行介绍

四、参考资料

PostgreSQL Type Conversion
PostgreSQL数据类型转换规则#1
PostgreSQL数据类型转换规则#2
PostgreSQL数据类型转换规则#3