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SQL join on multiple columns in same tables
... subqueries, but I'm having trouble joining columns together from the same tables. I tried:
2 Answers
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Auto Generate Database Diagram MySQL [closed]
... every project. Is there a tool out there that will let me select specific tables and then create a database diagram for me based on a MySQL database? Preferably it would allow me to edit the diagram afterward since none of the foreign keys are set...
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Count number of rows within each group
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An old question without a data.table solution. So here goes...
Using .N
library(data.table)
DT <- data.table(df)
DT[, .N, by = list(year, month)]
share
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SQL standard to escape column names?
...ing to SQLite,
'foo' is an SQL string
"foo" is an SQL identifier (column/table/etc)
[foo] is an identifier in MS SQL
`foo` is an identifier in MySQL
For qualified names, the syntax is: "t"."foo" or [t].[foo], etc.
MySQL supports the standard "foo" when the ANSI_QUOTES option is enabled.
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Django-DB-Migrations: cannot ALTER TABLE because it has pending trigger events
...s at the django shell. If you're looking for something more formal and testable, it depends on what versions you're using. If you use south, see: south.readthedocs.org/en/latest/tutorial/part3.html and if you use django's migrations, see the "data migrations" section here: docs.djangoproject.com/e...
In JavaScript, why is “0” equal to false, but when tested by 'if' it is not false by itself?
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Tables displaying the issue:
and ==
Moral of the story use ===
table generation credit: https://github.com/dorey/JavaScript-Equality-Table
sha...
Django - How to rename a model field using South?
...foo', 'full_name', 'name')
The first argument of db.rename_column is the table name, so it's important to remember how Django creates table names:
Django automatically derives the name of the database table from the name of your model class and the app that contains it. A model's database tabl...
How can I define a composite primary key in SQL?
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Just for clarification: a table can have at most one primary key. A primary key consists of one or more columns (from that table). If a primary key consists of two or more columns it is called a composite primary key. It is defined as follows:
CREATE...
SQL update query using joins
I have to update a field with a value which is returned by a join of 3 tables.
11 Answers
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What makes a SQL statement sargable?
...sts. It will literally have to evaluate this function for every row of the table. Much better to use:
WHERE myDate >= '01-01-2008' AND myDate < '01-01-2009'
Some other examples:
Bad: Select ... WHERE isNull(FullName,'Ed Jones') = 'Ed Jones'
Fixed: Select ... WHERE ((FullName = 'Ed Jones') ...