When I was started work on the PostgreSQL, crating first time a table, I become stuck on the Identity column because I was familiar with the MS SQL Server. So, first of all, I search the question, "Does Postgres automatically generate an id for every row?".
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The answer is Yes.
There are several ways you can generate the identity column in PostgreSQL, and some examples are given below
1- SERIAL and BIGSERIAL
Using serial and bigserial you can generate the identity column
Example:
--For the SERIAL CREATETABLEemployee ( empidserialNOTNULL,-- It's generate for the int nametext, addresstext, constraintpk_employee_empidPrimarykey(empid) ); --Insert some records INSERTINTOemployee(name,address)VALUES('Naina','Noida'); INSERTINTOemployee(name,address)VALUES('Ashish','Delhi'); --Now select statement SELECT*FROMemployee; |
In result you can see the ID is auto generates and increment by one
Result:
Same thing will happen with bigserial
--For the BIGSERIAL CREATETABLEemployee ( empidbigserialNOTNULL,-- it generate for the bigint nametext, addresstext, constraintpk_employee_empidPrimarykey(empid) ); |
2- GENERATED ALWAYS AS IDENTITY
Using GENERATED ALWAYS AS IDENTITY key we can generate the identity column, it automatically assign a unique value to a column which introduced as a new feature in PostgreSQL version 10.
Run the following query to re-create the employee table.
DROPTABLEIFEXISTSemployee; CREATETABLEemployee ( empidINTGENERATEDALWAYSASIDENTITY, nametextnotnull, addresstext, constraintpk_employee_empidPrimarykey(empid) ); Insertsomerecords INSERTINTOemployee(name,address)VALUES('Naina','Noida'); INSERTINTOemployee(name,address)VALUES('Ashish','Delhi'); |
Result:
