PostgreSQL源码解读（202）-查询#115(类型转换)
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 TABLE
testdb=# create table t_conv(id int);
CREATE TABLE
testdb=#
testdb=# insert into t_conv values(1);
INSERT 0 1
testdb=# insert into t_conv values(2);
INSERT 0 1
testdb=#
查询条件为id = ‘1’,’1’转换为int进行比较.
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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 = text
LINE 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.
testdb=# select oid,typname from pg_type where typname in ('int4','text');
oid | typname
-----+---------
23 | int4
25 | text
(2 rows)
testdb=# select oid,oprname,oprleft,oprright,oprresult,oprcode from pg_operator where oprname = '>' and oprleft = 23 and oprright = 25;
oid | oprname | oprleft | oprright | oprresult | oprcode
-------+---------+---------+----------+-----------+------------------
16407 | > | 23 | 25 | 16 | int_greater_text
(1 row)
testdb=# select oid,oprname,oprleft,oprright,oprresult,oprcode from pg_operator where oprname = '=' and oprleft = 23 and oprright = 25;
oid | oprname | oprleft | oprright | oprresult | oprcode
-----+---------+---------+----------+-----------+---------
(0 rows)
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.
*/
void
make_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_op
Breakpoint 2 at 0x619cdb: file parse_oper.c, line 762.
(gdb) c
Continuing.
Breakpoint 2, make_op (pstate=0x22d6e30, opname=0x22d6c48, ltree=0x22d7620, rtree=0x22d7678, last_srf=0x0, location=30)
at parse_oper.c:762
762 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) n
769 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) n
784 opform = (Form_pg_operator) GETSTRUCT(tup);
(gdb)
787 if (!RegProcedureIsValid(opform->oprcode))
(gdb) p *opform
$21 = {oid = 96, oprname = {data = "=", '\000' }, 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) n
798 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) n
830 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) n
Breakpoint 1, make_fn_arguments (pstate=0x22d6e30, fargs=0x22d76f8, actual_arg_types=0x7ffda1b2af80,
declared_arg_types=0x7ffda1b2af70) at parse_func.c:1835
1835 int i = 0;
(gdb)
调用coerce_type函数执行转换,unknown -> int4
(gdb) n
1837 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) n
1842 Node *node = (Node *) lfirst(current_fargs);
(gdb) n
1848 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) n
1873 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:840
840 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
网页题目：PostgreSQL源码解读（202）-查询#115(类型转换)
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