运算子不存在:json = json [英] Operator does not exist: json = json

问题描述

当我尝试从表中选择一些记录时

when I try to select some record from a table

    SELECT * FROM movie_test WHERE tags = ('["dramatic","women", "political"]'::json)

SQL代码产生错误

LINE 1: SELECT * FROM movie_test WHERE tags = ('["dramatic","women",...
                                        ^
HINT:  No operator matches the given name and argument type(s). You might      need to add explicit type casts.

********** 错误 **********

ERROR: operator does not exist: json = json
SQL 状态: 42883
指导建议:No operator matches the given name and argument type(s). You might need to add explicit type casts.
字符:37

我错过了什么吗?还是可以从中了解一些有关此错误的信息.

Did I miss something or where I can learn something about this error.

推荐答案

您无法比较json值.您可以改为比较文本值:

You cannot compare json values. You can compare text values instead:

SELECT * 
FROM movie_test 
WHERE tags::text = '["dramatic","women","political"]'

但是请注意，类型json的值以给出它们的格式存储为文本.因此，比较的结果取决于您是否始终采用相同的格式:

Note however that values of type json are stored as text in a format in which they are given. Thus the result of comparison depends on whether you consistently apply the same format:

SELECT 
    '["dramatic" ,"women", "political"]'::json::text =  
    '["dramatic","women","political"]'::json::text      -- yields false!

在Postgres 9.4+中，您可以使用jsonb类型解决此问题，该类型以分解的二进制格式存储.可以比较此类型的值:

In Postgres 9.4+ you can solve this problem using type jsonb, which is stored in a decomposed binary format. Values of this type can be compared:

SELECT 
    '["dramatic" ,"women", "political"]'::jsonb =  
    '["dramatic","women","political"]'::jsonb           -- yields true

因此该查询更加可靠:

SELECT * 
FROM movie_test 
WHERE tags::jsonb = '["dramatic","women","political"]'::jsonb

详细了解 JSON类型.

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