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How does Rails keep track of which migrations have run for a database?
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Rails creates a table in your database called schema_migrations to keep track of which migrations have run.
The table contains a single column, version. When Rails runs a migration, it takes the leading digits in the migration's file name a...
CSS table-cell equal width
I have an indeterminate number of table-cell elements inside a table container.
7 Answers
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SQL WITH clause example [duplicate]
...me assigned to the sub-query is treated as though it was an inline view or table. The SQL WITH clause is basically a drop-in replacement to the normal sub-query.
Syntax For The SQL WITH Clause
The following is the syntax of the SQL WITH clause when using a single sub-query alias.
WITH <alias_n...
How to change column datatype in SQL database without losing data
... 0 (BIT = false), anything else will be turned into 1 (BIT = true).
ALTER TABLE dbo.YourTable
ALTER COLUMN YourColumnName BIT
The other option would be to create a new column of type BIT, fill it from the old column, and once you're done, drop the old column and rename the new one to the old n...
ERROR 1452: Cannot add or update a child row: a foreign key constraint fails
I have created tables in MySQL Workbench as shown below :
21 Answers
21
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What is the difference between Left, Right, Outer and Inner Joins?
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Simple Example: Lets say you have a Students table, and a Lockers table. In SQL, the first table you specify in a join, Students, is the LEFT table, and the second one, Lockers, is the RIGHT table.
Each student can be assigned to a locker, so there is a LockerNumber co...
Filter by property
...(modelType, specify):
clause = "SELECT * from %s" % modelType._meta.db_table
if len(specify) > 0:
clause += " WHERE "
for field, eqvalue in specify.items():
clause += "%s = '%s' AND " % (field, eqvalue)
clause = clause [:-5] # remove last AND
pri...
Oracle: If Table Exists
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The best and most efficient way is to catch the "table not found" exception: this avoids the overhead of checking if the table exists twice; and doesn't suffer from the problem that if the DROP fails for some other reason (that might be important) the exception is still rai...
MySQL Select all columns from one table and some from another table
How do you select all the columns from one table and just some columns from another table using JOIN? In MySQL.
4 Answers
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What are the calling conventions for UNIX & Linux system calls (and user-space functions) on i386 an
...ABI in 64-bit code? It still truncates its inputs to 32-bit, so it's unsuitable for pointers, and it zeros r8-r11.
User Interface: function calling
x86-32 Function Calling convention:
In x86-32 parameters were passed on stack. Last parameter was pushed first on to the stack until all parameter...