Question

我有一个用户表，我希望将字符串列foo转换为带有{＆＃34; oldfield＆＃34;：＆lt; foo在当前行中的值＆gt;}，但我似乎无法找到正确的语法。我直接使用psql命令行界面。

这就是我的尝试：

 ALTER TABLE user_schema.user ALTER COLUMN "foo" SET DATA TYPE json USING '{"oldfield": "foo"}';

这会将字段更改为{＆＃34; oldfield＆＃34;：＆＃34; foo＆＃34;}，而不是foo列的实际值。我还尝试了以下组合，所有这些组合都因语法错误而失败。有任何想法吗？感谢

   ALTER TABLE user_schema.user ALTER COLUMN "foo" SET DATA TYPE json USING '{"oldfield": foo}';
ERROR:  invalid input syntax for type json
DETAIL:  Token "foo" is invalid.
CONTEXT:  JSON data, line 1: {"oldfield": foo...

 ALTER TABLE user_schema.user ALTER COLUMN "foo" SET DATA TYPE json USING '{"oldfield": \"foo\"}';
ERROR:  invalid input syntax for type json
DETAIL:  Token "\" is invalid.
CONTEXT:  JSON data, line 1: {"oldfield": \...
ALTER TABLE user_schema.user ALTER COLUMN "foo" SET DATA TYPE json USING '{"oldfield": 'foo'}';
ERROR:  syntax error at or near "foo"
LINE 1: ...Metadata" SET DATA TYPE json USING '{"oldfield": 'foo...
                                                             ^
ALTER TABLE user_schema.user ALTER COLUMN "foo" SET DATA TYPE json USING '{"oldfield": `foo`}';
ERROR:  invalid input syntax for type json
DETAIL:  Token "`" is invalid.
CONTEXT:  JSON data, line 1: {"oldfield": `...
 ALTER TABLE user_schema.user ALTER COLUMN "foo" SET DATA TYPE json USING '{"oldfield": user.foo}';
ERROR:  invalid input syntax for type json
DETAIL:  Token "user" is invalid.
CONTEXT:  JSON data, line 1: {"oldfield": user...
ALTER TABLE user_schema.user ALTER COLUMN "foo" SET DATA TYPE json USING '{"oldfield": user_schema.user.foo}';
ERROR:  invalid input syntax for type json
DETAIL:  Token "user_schema" is invalid.
CONTEXT:  JSON data, line 1: {"oldfield": user_schema...
ALTER TABLE user_schema.user ALTER COLUMN "foo" SET DATA TYPE json USING '{"oldfield": foo}';
ERROR:  invalid input syntax for type json
DETAIL:  Token "foo" is invalid.

Answer 1

使用功能json_build_object():

create table my_table(foo text);
insert into my_table values
    ('first'),
    ('second');

alter table my_table 
    alter column foo set data type json 
    using json_build_object('oldfield', foo);

select *
from my_table;

           foo           
-------------------------
 {"oldfield" : "first"}
 {"oldfield" : "second"}
(2 rows)

将postgres字符串列转换为json

1 个答案: