ALTER COLUMN Pname varchar(32) NOT NULL - 'not null' is requiredĪLTER TABLE. ALTER COLUMN PersonId NUMERIC(5,0) NOT NULL - 'not null' is requiredĪLTER TABLE. ALTER COLUMN PMid NUMERIC(5,0) NOT NULL - 'not null' is requiredĪLTER TABLE. You can write a trigger and do that or add virtual column in Mysql 5.7. So, future access to the table MUST specify a value instead of accepting a default. add new key/compound-key, fulfil the required non-null qualityĪLTER TABLE. At the point in time that I add the column the default/initial value is correct, but this can change over time. IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'.') )ĪLTER TABLE Person DROP CONSTRAINT PK_Person Select 1 from Person p group by PMid, PersonId, PName having COUNT(*) > 1 test your existing data suitable for new key or not Now the task he wants to accomplish is to execute a script to replace the existing compound-key with a new compound-key.įirst concern: the first requirement for fields to be a key is NOT NULL and they together need to be unique, otherwise you will get error when running the alter statement.įor that matter, I think the following is the right answer for the future answer seekers who have the same issue. He has an existing table with existing data and existing compound-key. I am surprised after all these years the answers to the question had not hit 100% what the question poster was asking. PRINT 'FSCK, need to figure out how to update NULL value(s).' PRINT 'FSCK, this column has duplicate keys, and can thus not be changed to primary key.' AND CONSTRAINT_NAME = 'PK_T_SYS_Language_Forms'ĪLTER TABLE T_SYS_Language_Forms ADD CONSTRAINT PK_T_SYS_Language_Forms PRIMARY KEY CLUSTERED (LANG_UID ASC) SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS IF 0 = (SELECT TOP 1 COUNT(*) AS cnt FROM T_SYS_Language_Forms GROUP BY LANG_UID ORDER BY cnt DESC) In this example, the table name is dbo.T_SYS_Language_Forms, and the column name is LANG_UID - First, chech if the table exists. Just in case anybody has as good a schema to work with as me. Now from DESCRIBE command, we can check the default. mysql> Alter table Student ADD(City Varchar(10) Default 'DELHI') Query OK, 5 rows affected (0.33 sec) Records: 5 Duplicates: 0 Warnings: 0. Hope this answer can help other SQL beginner. In the example below, with the help of ALTER Command, column ‘City’ is added with default value ‘DELHI’ to the table ‘Student’. So I research some document to find every detail. I got a little confuse when i have looked all answers. This can set constraint name by developer. Or the better one below ALTER TABLE Persion ADD CONSTRAINT PK_Persion PRIMARY KEY (PersionId,Pname,PMID) this: ALTER TABLE YourTable ADD YourNewColumn INT NOT NULL DEFAULT 10 WITH VALUES Add the column with null values first. The exact syntax depends on your database, but will will usually look like. MySQL / SQL Server / Oracle / MS Access: ALTER TABLE Persion ADD PRIMARY KEY (PersionId,Pname,PMID) This value will be used initially for all existing rows. Given constraint name when you created table,you can easily use You have to find the constraint name in your table. SQL Server / Oracle / MS Access: ALTER TABLE Persion Because there is one primary key for sql table.įirst, you have to drop your old primary key. You can't just add primary key,otherwise will cause error. UPDATE myTable SET dist = dbo.There is already an primary key in your table. if each parameter was split into and TABLE myTable ADD dist FLOAT DEFAULT(-1) - Change the table Question: Is there a postgres query to add a new column to an existing table and to automatically populate that column for all rows of the table with a certain value, lets say 'A1', just once, as the column is created, so that I can still set the DEFAULT value of the column to another value, lets say 'B2'. RETURN 123.45 - Do your calculation here, which would be a HUGE LOT easier INSERT INTO MyTable VALUES('', ''), ('', '')ĬREATE FUNCTION VARCHAR(20), VARCHAR(20)) It would make a lot more sense to split these into loc_1_x, loc_1_y, loc_2_x and loc_2_y, all of a numeric type such as FLOAT.įull example code (with loc_1 and loc_2 still as VARCHARs): CREATE TABLE MyTable (loc_1 VARCHAR(20), loc_2 VARCHAR(20)) The same also applies to loc_1 and loc_2, but then splitted. Then use UPDATE to set dist in each row to what it should be.Ī remark: dist looks numeric in value, so you should use a numeric datatype, and definitely not a VARCHAR type.You can specify a default value for all rows, but not different values for each row, and no formula either. First use ALTER to add the dist column.T-SQL does not support that, you'll need to split your command in multiple parts.
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