![]() SET contact_name = 'Mary Doe' WHERE id = 2 SET contact_name = 'John Doe' WHERE id = 1 Second, update the values in the contact_name column. When PostgreSQL added the column, this new column receive NULL, which violates the NOT NULL constraint.įirst, add the column without the NOT NULL constraint: ALTER TABLE customersĪDD COLUMN contact_name VARCHAR Code language: SQL (Structured Query Language) ( sql ) This is because the contact_name column has the NOT NULL constraint. PostgreSQL issued an error: ERROR: column "contact_name" contains null values Code language: SQL (Structured Query Language) ( sql ) ![]() Suppose that you want to add the contact_name column to the customers table: ALTER TABLE customersĪDD COLUMN contact_name VARCHAR NOT NULL Code language: SQL (Structured Query Language) ( sql ) ( 'Sony') Code language: SQL (Structured Query Language) ( sql ) The following statement inserts data into the customers table. Add a column with the NOT NULL constraint to a table that already has data To view the structure of the customers table in the psql tool, you can use the \d command like this: \d customers Code language: SQL (Structured Query Language) ( sql )Īs can be seen clearly from the output, the phone, fax, and email columns appeared at the end of the column list of the customers table. The following statement uses the ALTER TABLE ADD COLUMN statement to add the phone column to the customers table: ALTER TABLE customersĪDD COLUMN phone VARCHAR Code language: SQL (Structured Query Language) ( sql )Īnd the following statement adds the fax and email columns to the customers table: ALTER TABLE customersĪDD COLUMN email VARCHAR Code language: SQL (Structured Query Language) ( sql ) ) Code language: SQL (Structured Query Language) ( sql ) The following CREATE TABLE statement creates a new table named customers with two columns: id and customer_name: DROP TABLE IF EXISTS customers CASCADE To add multiple columns to an existing table, you use multiple ADD COLUMN clauses in the ALTER TABLE statement as follows: ALTER TABLE table_nameĪDD COLUMN column_name1 data_type constraint,ĪDD COLUMN column_name2 data_type constraint,ĪDD COLUMN column_namen data_type constraint Ĭode language: SQL (Structured Query Language) ( sql ) PostgreSQL ADD COLUMN statement examples PostgreSQL has no option to specify the position of the new column in the table. When you add a new column to the table, PostgreSQL appends it at the end of the table. Second, specify the name of the new column as well as its data type and constraint after the ADD COLUMN keywords.First, specify the name of the table that you want to add a new column to after the ALTER TABLE keyword.To add a new column to an existing table, you use the ALTER TABLE ADD COLUMN statement as follows: ALTER TABLE table_nameĪDD COLUMN new_column_name data_type constraint Code language: SQL (Structured Query Language) ( sql ) Introduction to the PostgreSQL ADD COLUMN statement Thou 8 digit is probably not necessary.Summary: in this tutorial, you will learn how to use the PostgreSQL ADD COLUMN statement to add one or more columns to an existing table. (Note: the max bigInt is 9223372036854775807 if you use 8 digit random number at the end, you can only have 922337203 records. However this will waste a huge amount of records. Insert into test_table (txt) values ('2') Insert into test_table (txt) values ('1') ![]() (so after the seq add a fix x digit random number): CREATE SEQUENCE test_seq ![]() The easiest way probably to use the sequence to guarantee uniqueness This is guaranteed error free solution not like other solutions on this thread INSERT INTO my_table (code) VALUES (new_code) if insert fails try again from step 1 CREATE OR REPLACE PROCEDURE my_table_insert() try to insert new record with new code and 3. Then we should have function or procedure (you can use code inside for trigger also) where we 1. ![]() One instance will INSERT and other will fail.įirst let us create table with code field and add unique index CREATE TABLE my_tableĬREATE UNIQUE INDEX ON my_table (lower(code)) Let us assume that we need unique code per record while inserting: Imagine two concurrent INSERTs are happening same time by miracle (which happens very often than you think) for both inserts same code was generated because at the moment of SELECT that code did not exist in table. All existing answers are WRONG because they are based on SELECT while generating unique index per table record. ![]()
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