我有一张看起来像这个来电者'makerar'的桌子
cname | wmname | avg
--------+-------------+------------------------
canada | zoro | 2.0000000000000000
spain | luffy | 1.00000000000000000000
spain | usopp | 5.0000000000000000
我想为每个cname选择最大平均值.
SELECT cname, wmname, MAX(avg) FROM makerar GROUP BY cname;
但我会收到一个错误,
ERROR: column "makerar.wmname" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT cname, wmname, MAX(avg) FROM makerar GROUP BY cname;
所以我这样做
SELECT cname, wmname, MAX(avg) FROM makerar GROUP BY cname, wmname;
但这不会给出意图的结果,并显示下面的错误输出.
cname | wmname | max
--------+--------+------------------------
canada …我正在尝试测试jsonPostgreSQL 9.3中的类型.
我在一个json名为data的表中调用了一列reports.JSON看起来像这样:
{
"objects": [
{"src":"foo.png"},
{"src":"bar.png"}
],
"background":"background.png"
}
我想查询表中所有与'objects'数组中'src'值匹配的报告.例如,是否可以在数据库中查询匹配的所有报告'src' = 'foo.png'？我成功写了一个可以匹配的查询"background":
SELECT data AS data FROM reports where data->>'background' = 'background.png'
但由于"objects"有一系列的价值观,我似乎无法写出有用的东西.是否可以在数据库中查询匹配的所有报告'src' = 'foo.png'？我查看了这些来源,但仍然无法得到它:
我也尝试过这样的事情,但无济于事:
SELECT json_array_elements(data->'objects') AS data from reports
WHERE data->>'src' = 'foo.png';
我不是SQL专家,所以我不知道我做错了什么.
想要查找某个json列包含空对象的所有行,{}.这可以使用JSON数组,或者如果我在对象中查找特定键.但我只是想知道对象是否为空.似乎找不到会这样做的运营商.
dev=# \d test
Table "public.test"
Column | Type | Modifiers
--------+------+-----------
foo | json |
dev=# select * from test;
foo
---------
{"a":1}
{"b":1}
{}
(3 rows)
dev=# select * from test where foo != '{}';
ERROR: operator does not exist: json <> unknown
LINE 1: select * from test where foo != '{}';
^
HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.
dev=# select * from …试图在带有rails的模式上做区别.
2.1.1 :450 > u.profiles.select("profiles.*").distinct
Profile Load (0.9ms) SELECT DISTINCT profiles.* FROM "profiles" INNER JOIN "integration_profiles" ON "profiles"."id" = "integration_profiles"."profile_id" INNER JOIN "integrations" ON "integration_profiles"."integration_id" = "integrations"."id" WHERE "integrations"."user_id" = $1 [["user_id", 2]]
PG::UndefinedFunction: ERROR: could not identify an equality operator for type json
LINE 1: SELECT DISTINCT profiles.* FROM "profiles" INNER JOIN "integ...
^
: SELECT DISTINCT profiles.* FROM "profiles" INNER JOIN "integration_profiles" ON "profiles"."id" = "integration_profiles"."profile_id" INNER JOIN "integrations" ON "integration_profiles"."integration_id" = "integrations"."id" WHERE "integrations"."user_id" = $1
ActiveRecord::StatementInvalid: …我正在尝试使用UNION规则在单个表上执行多个查询
我有两张桌子:
我希望首先得到一组pinned设置为的行,true并用最新的条目填充剩余的(pinned设置为false)
SELECT
project.id AS project_id,
project.name AS project_name,
array_agg(json_build_object('skill_id', project_skills.id,'name', project_skills.skill)) AS skills
from project
LEFT OUTER JOIN project_skills on project.name = project_skills.project
WHERE project.pinned = true
GROUP BY project_id,project_name
UNION
SELECT
project.id AS project_id,
project.name AS project_name,
array_agg(json_build_object('skill_id', project_skills.id,'name', project_skills.skill)) AS skills
from project
LEFT OUTER JOIN project_skills on project.name = project_skills.project
WHERE project.id != 1 AND project.pinned = false
GROUP BY project_id,project_name
ORDER …我在pg生产模式下收到此错误,但它在sqlite3开发模式下工作正常.
ActiveRecord::StatementInvalid in ManagementController#index
PG::Error: ERROR: column "estates.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT "estates".* FROM "estates" WHERE "estates"."Mgmt" = ...
^
: SELECT "estates".* FROM "estates" WHERE "estates"."Mgmt" = 'Mazzey' GROUP BY user_id
@myestate = Estate.where(:Mgmt => current_user.Company).group(:user_id).all
最近升级到使用PostgreSQL 9.3.1来利用JSON功能.在我的表中,我有一个json类型的列,其结构如下:
{
"id": "123",
"name": "foo",
"emails":[
{
"id": "123",
"address": "somethinghere"
},
{
"id": "456",
"address": "soemthing"
}
]
}
这只是用于问题目的的虚拟数据.
是否可以根据ID查询电子邮件数组中的特定项？
差不多:"返回id = 123的电子邮件""？