SQL Constraints
Constraints can be specified when the table is created (inside the CREATE TABLE statement) or after the table is created (inside the ALTER TABLE statement). Ensures that a column (or combination of two or more columns) have an unique identity which helps to find a particular record in a table more easily and quickly FOREIGN KEY - Ensure the referential integrity of the data in one table to match values in another table CHECK - Ensures that the value in a column meets a specific condition DEFAULT - Specifies a default value when specified none for this column The next chapters will describe each constraint in detail
DELETE is not a DML-operation which support bulk logging and if a table does not have constraints which prevents a TRUNCATE than the following workload seems to be the best by consideration of bulk logged operations: Separate the data which should not be deleted by using SELECT ... Use of TRUNCATE instead of DELETE for the deletion of records The usage of TRUNCATE instead of DELETE seems to be inviting, because TRUNCATE does not log the deletion of each record
MySQL :: MySQL 5.1 Reference Manual :: 13.1.7 ALTER TABLE Syntax
Updates and writes to the table that begin after the ALTER TABLE operation begins are stalled until the new table is ready, then are automatically redirected to the new table without any failed updates. For example, adding a member to a SET column that has 8 members changes the required storage per value from 1 byte to 2 bytes; this will require a table copy
ALTER TABLE only allows columns to be added that can contain nulls, or have a DEFAULT definition specified, or the column being added is an identity or timestamp column, or alternatively if none of the previous conditions are satisfied the table must be empty to allow addition of this column. Fill in your details below or click an icon to log in: Email (required) (Address never made public) Name (required) Website You are commenting using your WordPress.com account
PostgreSQL: Documentation: 9.0: ALTER TABLE
(This requires superuser privilege if any of the triggers are internally generated constraint triggers such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints.) USER Disable or enable all triggers belonging to the table except for internally generated constraint triggers such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints. Because of this flexibility, the USING expression is not applied to the column's default value (if any); the result might not be a constant expression as required for a default
MySQL :: MySQL 5.6 Reference Manual :: 13.1.7 ALTER TABLE Syntax
These keywords are deprecated beginning with MySQL Cluster NDB 7.3; they continue to be supported in MySQL Cluster NDB 7.4, but are subject to removal in a future version of MySQL Cluster. Updates and writes to the table that begin after the ALTER TABLE operation begins are stalled until the new table is ready, then are automatically redirected to the new table without any failed updates
PostgreSQL: Documentation: 9.1: ALTER TABLE
(This requires superuser privilege if any of the triggers are internally generated constraint triggers such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints.) USER Disable or enable all triggers belonging to the table except for internally generated constraint triggers such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints. The value of separating validation from initial creation is that you can defer validation to less busy times, or can be used to give additional time to correct pre-existing errors while preventing new errors
The post prompted me to revisit the Books On Line page for the ALTER TABLE statement and with subsequent research, I realized that SQL Server actually empowers us with different methods to work with default values depending upon whether we are adding a new column to an existing table or when we are altering an existing column. Adding a new column to an existing table If the column is being added to an existing table and has a default definition available, then the ALTER TABLE statement allows us to use the WITH VALUES clause to store the default value in each existing record of the table
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sql server - Why does ALTER COLUMN to NOT NULL cause massive log file growth? - Database Administrators Stack Exchange
But it's clear that - while both the update operation and the addition of the NOT NULL constraint undeniably write to the page - the latter does so in an entirely different way. On databases with one of the snapshot isolation options enabled then the versioning information in each row is updated (@SQL Kiwi points out that this can also occur in databases without SI enabled as described here)
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