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how to exclude null values in array_agg like in string_agg using postgres?
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SQL Fiddle
select
id,
(select array_agg(a) from unnest(canonical_users) a where a is not null) canonical_users,
(select array_agg(a) from unnest(non_canonical_users) a where a is not null) non_canonical_users
fro...
Cast int to varchar
...m t9;
select CONVERT(id, CHAR(50)) as colI1
from t9;
See the following SQL — in action — over at SQL Fiddle:
/*! Build Schema */
create table t9 (id INT, name VARCHAR(55));
insert into t9 (id, name) values (2, 'bob');
/*! SQL Queries */
select CAST(id as CHAR(50)) as col1 from t9;
select C...
SensorUtil 传感器工具扩展：在后台和屏幕关闭时保持传感器工作 · App Inv...
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此组件是通用平均器，可用于任何数值的平滑处理，包括不被 UrsSensorAverager 支持的传感器（如 MagneticFieldSensor）。
属性 Properties
平均值 Average
计算算术平均值。
缓存大小 CacheSize
要聚合的值的数量...
How can I drop all the tables in a PostgreSQL database?
How can I drop all tables in PostgreSQL, working from the command line?
24 Answers
24
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updating table rows in postgres using subquery
...FROM (SELECT address_id, customer, address, partn
FROM /* big hairy SQL */ ...) AS subquery
WHERE dummy.address_id=subquery.address_id;
This syntax is not standard SQL, but it is much more convenient for this type of query than standard SQL. I believe Oracle (at least) accepts something sim...
How do I execute inserts and updates in an Alembic upgrade script?
...rent connection, and make a session with it.
Or use bind.execute() to use SQLAlchemy's lower level to write SQL queries directly. This is useful for simple migrations.
Use the models and session as you normally would in your application.
"""create teams table
Revision ID: 169ad57156f0
Revises...
I need to generate uuid for my rails application. What are the options(gems) I have? [duplicate]
... UUID has RFC! This will break any UUID validation (like in PostgreSQL)
– kixorz
Feb 10 '14 at 8:05
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CASCADE DELETE just once
I have a Postgresql database on which I want to do a few cascading deletes. However, the tables aren't set up with the ON DELETE CASCADE rule. Is there any way I can perform a delete and tell Postgresql to cascade it just this once? Something equivalent to
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Does PostgreSQL support “accent insensitive” collations?
In Microsoft SQL Server, it's possible to specify an "accent insensitive" collation (for a database, table or column), which means that it's possible for a query like
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What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
...lly, a lot of dbms have been quite poor when it comes to handling joins (MySQL being a particularly noteworthy example). So n+1 has, often, been notably faster than a join. And then there are ways to improve on n+1 but still without needing a join, which is what the original problem relates to.
How...