We can alternatively use the MAX() function instead of the MIN() function to change which rows are deleted. To verify the result, we can select all remaining rows in the table: SELECT * FROM Dogs To remove those duplicate rows, we can switch the SELECT * to DELETE and remove the ORDER BY clause: DELETE FROM Dogs The other Wag Johnson will remain in the database. For example, the table contains three dogs called Wag Johnson, but there are only two Wag Johnson’s listed here – the two that will be deleted. For each set of duplicates listed here, there’s one that’s not listed (and will not be deleted). What I mean is that, these are the actual rows that will be deleted. These are the excess rows from the list of duplicates. We can start by finding all rows that should be deleted: SELECT * FROM Dogs Therefore, in this article we ignore the primary key and delete rows that contain duplicate values across the remaining columns. But in real life situations, you will often want to de-dupe tables that contain primary keys. The DogId column holds unique values (because it’s the table’s primary key), and therefore, strictly speaking, there are no duplicates. We can see that the first two rows are duplicates, as well as the last three rows. Our examples use the following data: SELECT * FROM Dogs So in the case of say, three identical rows, it deletes two and keeps one. The following examples delete duplicate rows but keep one. The primary key is used in the query, but it’s ignored when comparing duplicates (due to the fact that primary keys prevent duplicate rows by definition). Try the below command to create a table and the table will be created efficiently as seen in the image below.Below are two options for removing duplicate rows from a table in PostgreSQL when those rows have a primary key or unique identifier column. On the other hand, the column “name” is defined as the TEXT NOT NULL data type. The column “id” has been defined as the primary key column as its datatype is SERIAL. Example 01:Ĭreate a table “Test” with two columns “id” and “name”. But when we use the keyword SERIAL in our query while creating a table, we shouldn’t need to add primary column values while inserting the values. This means we have to add the values to the primary key column while using the INSERT statement. When we create a table, we usually don’t add the keyword SERIAL in the primary column field. Type your password for the selected username and hit “Enter” from the keyboard to start using the command shell. Leave it to default if you don’t want to change it. In the end, you have to provide the username for the database you choose. You can also work on the default port 5432, but you can also change it. We will be using the “test” database, that’s why we have added it. If you don’t want to change it then left it as default. Write the database name that lies in your server on which you want to work on. Add your server name on which you want to work on, otherwise left it to default. Open the PostgreSQL command-line shell from the desktop. To get the concept of auto-increment, please ensure PostgreSQL is mounted and configured on your system before continuing with the illustrations in this guide. If the id field or the table itself is omitted, the sequence will be discarded. The id field will be allocated as the holder of the series.PostgreSQL applies the implicit restriction NOT NULL to an id field since a series produces numeric values.It produces the next value in the series and sets it as the field’s default reference value. PostgreSQL generates a series entity first.Let us now glance at the CREATE TABLE declaration in more detail:
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