我有一个比较两个hstore列的视图。
当我转储并恢复此数据库时，还原失败并显示以下错误消息：
Importing /tmp/hstore_test_2014-05-12.backup...
pg_restore: [archiver (db)] Error while PROCESSING TOC:
pg_restore: [archiver (db)] Error from TOC entry 172; 1259 1358132 VIEW hstore_test_view xxxx
pg_restore: [archiver (db)] could not execute query: ERROR: operator does not exist: public.hstore = public.hstore
LINE 2: SELECT NULLIF(hstore_test_table.column1, hstore_test_table....
^
HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.
Command was: CREATE VIEW hstore_test_view AS
SELECT NULLIF(hstore_test_table.column1, hstore_test_table.column2) AS "nullif"
FROM hst...
pg_restore: [archiver (db)] could not execute query: ERROR: relation "hstore_test_schema.hstore_test_view" does not exist
Command was: ALTER TABLE hstore_test_schema.hstore_test_view OWNER TO xxxx;
我能够通过以下步骤在PostgreSQL 9.3.0中创建此错误：
CREATE DATABASE hstore_test;
\c hstore_test
CREATE EXTENSION hstore WITH SCHEMA public;
CREATE SCHEMA hstore_test_schema;
CREATE TABLE hstore_test_schema.hstore_test_table(
id int,
column1 hstore,
column2 hstore,
PRIMARY KEY( id )
);
CREATE VIEW hstore_test_schema.hstore_test_view AS
SELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;
为了完整性，转储和恢复过程如下所示：
pg_dump -U xxxx -h localhost -f /tmp/hstore_test_2014-05-12.backup -Fc hstore_test
psql -U xxxx -h localhost -d postgres -c "DROP DATABASE hstore_test"
psql -U xxxx -h localhost -d postgres -c "CREATE DATABASE hstore_test"
pg_restore -U xxxx -h localhost -d hstore_test /tmp/hstore_test_2014-05-12.backup
pg_restore -l /tmp/hstore_test_2014-05-12.backup建议在创建视图之前启用hstore扩展名：
;
; Archive created at Mon May 12 11:18:32 2014
; dbname: hstore_test
; TOC Entries: 15
; Compression: -1
; Dump Version: 1.12-0
; Format: CUSTOM
; Integer: 4 bytes
; Offset: 8 bytes
; Dumped from database version: 9.3.0
; Dumped by pg_dump version: 9.3.0
;
;
; Selected TOC Entries:
;
2074; 1262 1358002 DATABASE - hstore_test xxxx
7; 2615 1358003 SCHEMA - hstore_test_schema xxxx
5; 2615 2200 SCHEMA - public postgres
2075; 0 0 COMMENT - SCHEMA public postgres
2076; 0 0 ACL - public postgres
173; 3079 11787 EXTENSION - plpgsql
2077; 0 0 COMMENT - EXTENSION plpgsql
174; 3079 1358004 EXTENSION - hstore
2078; 0 0 COMMENT - EXTENSION hstore
171; 1259 1358124 TABLE hstore_test_schema hstore_test_table xxxx
172; 1259 1358132 VIEW hstore_test_schema hstore_test_view xxxx
2069; 0 1358124 TABLE DATA hstore_test_schema hstore_test_table xxxx
1960; 2606 1358131 CONSTRAINT hstore_test_schema hstore_test_table_pkey xxxx
顺便说一下，将NULLIF(col1, col2)替换为col1 = col2似乎会使错误消失，尽管事实上它是pg_restore所抱怨的明确比较。
答案 0 :(得分：9)
这是一个PostgreSQL错误。 I have relayed your report to the pgsql-bugs list
正在发生的事情是pg_dump在您的架构中创建表时设置search_path以排除public。这个是正常的。当它转储引用不在search_path上的内容的对象时，它会明确地对它们进行模式限定，以便它们起作用。
适用于=案例，因为pg_dump在这种情况下看到=实际上是OPERATOR(public.=)，并将其转储为该格式：
CREATE VIEW hstore_test_view AS
SELECT (hstore_test_table.column1 OPERATOR(public.=) hstore_test_table.column2) AS comparison
FROM hstore_test_table;
但是，pg_dump无法通过nullif伪函数隐式使用的运算符执行此操作。这导致以下伪造的命令序列：
CREATE EXTENSION IF NOT EXISTS hstore WITH SCHEMA public;
...
SET search_path = hstore_test_schema, pg_catalog;
...
CREATE VIEW hstore_test_view AS
SELECT NULLIF(hstore_test_table.column1, hstore_test_table.column2) AS comparison
FROM hstore_test_table;
pg_dump只使用pg_catalog.pg_get_viewdef函数转储视图，因此这可能需要服务器后端修复。
最简单的解决方法是不使用nullif，将其替换为更详细但等效的case：
CASE WHEN column1 = column2 THEN NULL ELSE column1 END;
语法没有像我们使用显式nullif那样提供对OPERATOR(public.=)伪函数运算符进行模式限定的方法，因此修复似乎并不简单。
我预计同样的问题会影响GREATEST和LEAST，也许也会影响DISTINCT，但事实并非如此。两者似乎都找到了他们所需的运算符，即使它们在运行时不在search_path，但如果运算符在视图定义时不在search_path上，则不会失败。这表明他们可能正在使用类型的b-tree运算符类来查找运算符，通过表中的类型条目（通过表的属性找到）。 （更新：检查来源，是的，这就是他们所做的）。据推测，nullif也应该这样做，但事实并非如此。
相反它死在：
hstore_test=# \set VERBOSITY verbose
hstore_test=# CREATE VIEW hstore_test_schema.hstore_test_view AS
SELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;
ERROR: 42883: operator does not exist: public.hstore = public.hstore
LINE 2: SELECT NULLIF(column1, column2) AS comparison FROM hstore_te...
^
HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.
LOCATION: op_error, parse_oper.c:722
当我在那里设置断点时，陷阱在：
Breakpoint 1, op_error (pstate=pstate@entry=0x1189f38, op=op@entry=0x1189c10, oprkind=oprkind@entry=98 'b', arg1=arg1@entry=97207, arg2=arg2@entry=97207,
fdresult=FUNCDETAIL_NOTFOUND, location=location@entry=58) at parse_oper.c:706
706 {
(gdb) bt
#0 op_error (pstate=pstate@entry=0x1189f38, op=op@entry=0x1189c10, oprkind=oprkind@entry=98 'b', arg1=arg1@entry=97207, arg2=arg2@entry=97207, fdresult=FUNCDETAIL_NOTFOUND,
location=location@entry=58) at parse_oper.c:706
#1 0x000000000051a81b in oper (pstate=pstate@entry=0x1189f38, opname=opname@entry=0x1189c10, ltypeId=ltypeId@entry=97207, rtypeId=rtypeId@entry=97207,
noError=noError@entry=0 '\000', location=location@entry=58) at parse_oper.c:440
#2 0x000000000051ad34 in make_op (pstate=pstate@entry=0x1189f38, opname=0x1189c10, ltree=ltree@entry=0x118a528, rtree=0x118a590, location=58) at parse_oper.c:770
#3 0x00000000005155e1 in transformAExprNullIf (a=0x1189bc0, pstate=0x1189f38) at parse_expr.c:1021
#4 transformExprRecurse (pstate=pstate@entry=0x1189f38, expr=0x1189bc0) at parse_expr.c:244
#5 0x0000000000517484 in transformExpr (pstate=0x1189f38, expr=<optimized out>, exprKind=exprKind@entry=EXPR_KIND_SELECT_TARGET) at parse_expr.c:116
#6 0x000000000051ff30 in transformTargetEntry (pstate=pstate@entry=0x1189f38, node=0x1189bc0, expr=expr@entry=0x0, exprKind=exprKind@entry=EXPR_KIND_SELECT_TARGET,
colname=0x1189ba0 "comparison", resjunk=resjunk@entry=0 '\000') at parse_target.c:94
#7 0x00000000005212df in transformTargetList (pstate=pstate@entry=0x1189f38, targetlist=<optimized out>, exprKind=exprKind@entry=EXPR_KIND_SELECT_TARGET)
at parse_target.c:167
#8 0x00000000004ef594 in transformSelectStmt (stmt=0x11899f0, pstate=0x1189f38) at analyze.c:942
#9 transformStmt (pstate=0x1189f38, parseTree=0x11899f0) at analyze.c:243
#10 0x00000000004f0a2d in parse_analyze (parseTree=0x11899f0,
sourceText=sourceText@entry=0x114e6b0 "CREATE VIEW hstore_test_schema.hstore_test_view AS\nSELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;", paramTypes=paramTypes@entry=0x0, numParams=numParams@entry=0) at analyze.c:100
#11 0x000000000057cc4e in DefineView (stmt=stmt@entry=0x114f7e8,
queryString=queryString@entry=0x114e6b0 "CREATE VIEW hstore_test_schema.hstore_test_view AS\nSELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;") at view.c:385
#12 0x000000000065b1cf in ProcessUtilitySlow (parsetree=parsetree@entry=0x114f7e8,
queryString=0x114e6b0 "CREATE VIEW hstore_test_schema.hstore_test_view AS\nSELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;",
context=<optimized out>, params=params@entry=0x0, completionTag=completionTag@entry=0x7fffc98c9990 "", dest=<optimized out>) at utility.c:1207
#13 0x000000000065a54e in standard_ProcessUtility (parsetree=0x114f7e8, queryString=<optimized out>, context=<optimized out>, params=0x0, dest=<optimized out>,
completionTag=0x7fffc98c9990 "") at utility.c:829
所以直接问题看起来像transformAExprNullIf无法通过b-tree opclass和typecache使用其操作数的类型来查找运算符。