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When to use SELECT … FOR UPDATE?
Please help me understand the use-case behind SELECT ... FOR UPDATE .
2 Answers
2
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Can I use a function for a default value in MySql?
... update previously existing rows, like this:
UPDATE app_users SET uuid = (SELECT uuid());
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How can I get column names from a table in SQL Server?
... much more by querying the Information Schema views.
This sample query:
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = N'Customers'
Can be made over all these DB objects:
CHECK_CONSTRAINTS
COLUMN_DOMAIN_USAGE
COLUMN_PRIVILEGES
COLUMNS
CONSTRAINT_COLUMN_USAGE
CONSTRAINT_...
Best database field type for a URL
...
The URL really might break the 65,535 byte row limit
Your queries won't select or update a bunch of URLs at once (or very often). This is because TEXT columns just hold a pointer inline, and the random accesses involved in retrieving the referenced data can be painful.
...
Find the number of columns in a table
...
SELECT COUNT(*)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_catalog = 'database_name' -- the database
AND table_name = 'table_name'
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SQLAlchemy IN clause
...3,456))).all()
edit: Without the ORM, it would be
session.execute(
select(
[MyUserTable.c.id, MyUserTable.c.name],
MyUserTable.c.id.in_((123, 456))
)
).fetchall()
select() takes two parameters, the first one is a list of fields to retrieve, the second one is the where ...
PHP date() format when inserting into datetime in MySQL
...FROM_UNIXTIME(1231634282));
Query OK, 1 row affected (0.00 sec)
mysql> select * from a_table;
+---------------------+
| a_date |
+---------------------+
| 2009-01-10 18:38:02 |
+---------------------+
shar...
Create table (structure) from existing table
...
Try:
Select * Into <DestinationTableName> From <SourceTableName> Where 1 = 2
Note that this will not copy indexes, keys, etc.
If you want to copy the entire structure, you need to generate a Create Script of the tab...
MySQL Creating tables with Foreign Keys giving errno: 150
...h a value in the Parent table PK column(s). Check this with a query like:
SELECT COUNT(*) FROM Child LEFT OUTER JOIN Parent ON Child.FK = Parent.PK
WHERE Parent.PK IS NULL;
This must return zero (0) unmatched values. Obviously, this query is an generic example; you must substitute your table nam...
Extract a dplyr tbl column as a vector
...2 3.62 3.54 4.11
A nice way to do this in v0.2 of dplyr:
iris2 %>% select(Species) %>% collect %>% .[[5]]
Or if you prefer:
iris2 %>% select(Species) %>% collect %>% .[["Species"]]
Or if your table isn't too big, simply...
iris2 %>% collect %>% .[["Species"]]
...