![]() If you cannot get out of that then consider leaving it as a NULL-able column. In the case where you add it is NULL-able and backfill it, making the column NOT NULL will still lock the table while the engine checks every row to make sure it is NOT NULL so you'll still need some downtime. Pick a time when you can add the column in the way Gail showed, maybe as part of a scheduled reboot or other downtime, or look at Chris' method where the column is added as NULL-able but chunk the update to fill in the column with 0's into small batches of 10K rows or so at a time so you do not block too many users while you backfill the data. You should be more concerned that when you add the column that no data is lost in the process. The table in question receives both a lot of reads and writes, this is my concern. ![]() Good point completely overlooked the fact that the table will be written to during the read to the new table :ermm: douh! 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. 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. Yes definitely slower and more work but it wont lock the table.Įrr, I presume you re worried about locking the table because people are using it. You can do that, it'll likely be slower than the ALTER and far more work, but it'll do the job. For example, we try to add the column product_stock which already exist in the table.That is why I was looking into creating a new table with the addtional column then moving the data etc and finally doing a table rename The column you are adding to the table must not exist otherwise MySQL will issue an error. SELECT * FROM Products Īs you can see the product_date column is populated with the default value which is. Now we can check the Products table again. In this case, MySQL adds the column using default values. However, the Products table already has data. Please note that the column product_date is defined as NOT NULL and we haven’t provided any default value for that. ALTER TABLE ProductsĪDD COLUMN product_stock int DEFAULT '0', We can check the Products table using the SELECT statement to see the changes.įourth, we will add two columns product_stock and product_date to the Products table using the single statement. VALUES('Keyboard','Wireless keyboard',20), INSERT INTO Products (product_name, product_description, product_price) Now insert some records into the Products table. In the above statement, we have added a new column product_description after the product_name column. ALTER TABLE ProductsĪDD COLUMN product_description varchar(255) AFTER product_name Third, we add a new column product_description. Here, we haven’t mentioned the position of the new column. ALTER TABLE ProductsĪDD COLUMN product_price decimal(10,2) NOT NULL Second, we will add one column named product_price. ![]() Product_id int AUTO_INCREMENT PRIMARY KEY, Let’s understand the concept of MySQL ADD COLUMN with some examples to understand the topic in depth.įirst, we will create a table named Products with two columns: product_id and product_name. Here, each ADD COLUMN statement is separated by a comma( ,). To add more than one column, you use the following syntax: ALTER TABLE tableĪDD column_name_1 column_1_definition ,ĪDD column_name_2 column_2_definition , By default, MySQL adds a column to the last position. Also, you can specify the name column after the AFTER keyword if you want to insert the new column after a specific column. You can use FIRST to insert the new column in the first position. That means after which column you want to add the new column. Third, optionally, you can specify the position of the new column. Here, the COLUMN keyword is optional, you can omit it if you want. Second, specify the name of the new column along with the column definition after the ADD COLUMN keywords. Let’s understand the above syntax in more detail.įirst, you specify the name of the column after the ALTER TABLE keywords. ALTER TABLE table_nameĪDD column_name column_definition The below syntax is to add a column to a table in MySQL. You can also add more than one column to a table using this statement. CREATE TABLE extraColumn ( att1 float NULL ,att2 float NULL ,extra AS 0.0 PERSISTED ) Share. CREATE TABLE extraColumn ( att1 float NULL ,att2 float NULL ,extra AS 0.0 ) But if you need that, you can persist it. Then it does not have to be a real column. ![]() MySQL allows us to add a column to an existing table using the MySQL ALTER TABLE ADD COLUMN statement. I understand this column will always have value of 0.0. ![]() Summary: in this tutorial, you will learn how to add one or more columns to an existing table using the MySQL ADD COLUMN statement. ![]()
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