PowerBuilder Tips
SystemKey When the insertion point is not in a line edit and the user presses ALT or ALT + another key Timer When a specified number of seconds elapses after the Timer function has been called
SQLite Query Language: ALTER TABLE
If any views refer to table X in a way that is affected by the schema change, then drop those views using DROP VIEW and recreate them with whatever changes are necessary to accommodate the schema change using CREATE VIEW. If foreign key constraints are enabled when a table is renamed, then any REFERENCES clauses in any table (either the table being renamed or some other table) that refer to the table being renamed are modified to refer to the renamed table by its new name
PostgreSQL: Documentation: 9.4: ALTER TABLE
VALIDATE CONSTRAINT This form validates a foreign key or check constraint that was previously created as NOT VALID, by scanning the table to ensure there are no rows for which the constraint is not satisfied. (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
Pinal, as probably the most dedicated SQL teacher online what the reason behind tables with NULL values at all except the fact they take less HDD space than 0 for instance? It is much harder to maintain those in ASP.NET later on. He replied with another question, asking whether there is any existing short method that he can use to add a column which is not null and can be populated with some specific values
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
adding a new not null bit column with default 0
Is it only for reads? If you do not lock the table the "copy" and "rename" steps then if anyone modifies data in the source table during the process you could lose data when you drop the old table and rename the new one to take its place.The method Gail showed is your best bet for performance and protect against data loss unless you are OK with losing data or you know your table is truly only ever read
In the pre-11g releases, adding a new not null column with a default value would have caused a massive update on the entire table, locking it for the operation and generating tons of undo and redo
Alter Table Add Column
Create Table Dynamically Drop Table Constraints Add Column Constraint Rename Column Using ALTER INDEX Find Column in All Databases Post a comment Comments (RSS) Trackback Permalink Click here to cancel reply. Reply to this comment najib 25 Jun 2014 at 11:09 am ok i found this info here usefull and simple to understand thank you Reply to this comment Home Tuning Services Featured Articles How to cache stored procedure results using a hash key There are a lot of different design patterns that lend themselves to creating SQL Server Database Optimization Guide In the troubleshooting guide we went over the different physical bottlenecks that can Yet Another Temp Tables Vs Table Variables Article The debate whether to use temp tables or table variables is an old Using Union Instead of OR Sometimes slow queries can be rectified by changing the query around a bit
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)
Add a column, with a default value, to an existing table in SQL Server - Stack Overflow
A much more thorough SQL script to add a column with a default value is below including checking if the column exists before adding it also checkin the constraint and dropping it if there is one
This -- Trying to add a NOT NULL column without a default ALTER TABLE DefaultTest ADD NotNull2 char(1) NOT NULL GO Returns an error of Msg 4901, Level 16, State 1, Line 1 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
Oracle database 11g offers a new quick, easy, instant solution; instead of updating ALL the rows of the table, Oracle 11g now updates the metadata only
No comments:
Post a Comment