Introduction to PostgreSQL group_concat

PostgreSQL group_concat Function is not available but we have used same function as array_agg and array_to_string to work same as group_concat function in PostgreSQL. There is no function available in PostgreSQL of group_concat but we have used array_agg and array_to_string to work same as group_concat which function is available in MySQL. Array_agg function in PostgreSQL will return the elements of group of array and array_to_string function will concatenate all the values of array using separator used in query.

Syntax of PostgreSQL group_concat

Below is the syntax :

Select name_of_column1, name_of_column2, name_of_column3, ….., name_of_columnN array_to_string (array_agg (name_of_column), “Value separator”) from name_of_table JOIN condition Group by condition;

Below is the parameter description:

• Select: This operation is used to select the column value to concatenate by using the array_to_string and array_agg function in PostgreSQL. We can select single as well as multiple column with array_agg function.
• Name of column: This is defined as select the name of column from the table to retrieve and concatenate the data of column by using the array_to_string and array_agg function in PostgreSQL.
• Array_to_string: This function in PostgreSQL works same as group_concat function which was used in other database. We can use this function by using the array_agg function in PostgreSQL. Both the function together same work as group_concat function.
• Array_agg: This function in PostgreSQL works same as group_concat function which was used in other database. This function is basically used to return the element from group of array. This function is very important in PostgreSQL to concatenate the column values.
• Value separator: This is defined as separate column value by using the separator, basically we can use ‘,’, ‘;’, etc.to separate the column values by using the array_to_string and array_agg function in PostgreSQL.
• Name of table: This is defined as select the name of table from which we have retrieve column values and concatenate the data of column by using the array_to_string and array_agg function in PostgreSQL.
• Join condition: This is defined as use join condition to concatenate two specific table column data in PostgreSQL. We have use join operations with array_to_string and array_agg function in PostgreSQL.
• Group by condition: This condition is used with array_to_string and array_agg function in PostgreSQL.

How group_concat Function works in PostgreSQL?

• Basically group_concat function is not available in PostgreSQL which was available in MySQL. Instead of using group_concat in PostgreSQL we are using array_to_string and array_agg function.
• Array_agg function is basically used to retrieve element of array from the table. Using this function we are retrieving the column array elements value.

Below example shows that after using array_agg function we can only retrieve the array elements from the column.

Code:

select id, array_agg(name) from stud2 group by id;
select * from stud2;

Output:

• Above figure shows that we are using array_agg function on name column after using this function on name column it will only display all values from the column in array element format.
• Array_to_string function is basically used to combine the values from table column which was retrieve from array element by using the array_agg function in PostgreSQL.
• Using Array_to_string function and array_agg function, we have combine the column rows using separator.
• Value separator is very useful and important while using Array_to_string and array_agg function in PostgreSQL.
• We have also use the string_agg function to concatenate column values in PostgreSQL. String_agg function is very useful and important while concatenating column values in PostgreSQL.
• We need to use group by clause with array_to_string function and array_agg function in PostgreSQL, if we have not used group by clause it will issue error.

Below example shows that we need to use group by clause with Array_to_string function and array_agg function in PostgreSQL.

Code:

select name, array_to_string(array_agg(name), ',') from stud2;
select name, array_to_string(array_agg(name), ',') from stud2 group by name;

Output:

• In above first example we have not used group by clause then it will issue error. After using group by will not issue error, it will display concatenated output of column values.

Examples of PostgreSQL group_concat

We are using group_concat table to describe example of group_concat function in PostgreSQL.

Below is the data and table description of group_concat table.

Code:

select * from group_concat;
\d+ group_concat;

Output:

Example #1

Group concat using the string_agg function.

• Below example shows that concatenate table column by using string_agg function.
• We are concatenating name column from group_concat table.

Code:

select string_agg(CAST(name AS varchar), ',') from group_concat;
select string_agg(CAST(name AS varchar), ',') from group_concat group by name;

Output:

Example #2

Group concat using array_agg and array_to_string function.

• Below example shows that concat table column by using array_agg and array_to_string function in PostgreSQL.
• We have concatenating name column from group_concat table.

Code:

select name, array_to_string(array_agg(name), ',') from group_concat group by name;
select name, array_to_string(array_agg(name), '”') from group_concat group by name;

Output:

Example #3

Group concat to order each column using array_agg and array_to_string function.

• Below example shows that group concat to order each column using array_agg and array_to_string function in PostgreSQL.
• We have used name and address column from the group_concat table.

Code:

select address, array_to_string(array_agg(name order by name), '"') from group_concat group by address;
select address, array_to_string(array_agg(name order by name), ',') from group_concat group by address;

Output:

Conclusion

There is no function like group_concat available in PostgreSQL which was available in MySQL, instead of using this function we are using array_agg and array_to_string function. Array_agg and array_to_string function will work same as group_concat function work in other databases. We can also use string_agg function in PostgreSQL.

This is a guide to PostgreSQL group_concat. Here we discuss the introduction to PostgreSQL group_concat , how group_concat function works with query examples. You may also have a look at the following articles to learn more –

1. PostgreSQL Materialized Views
2. PostgreSQL UNIQUE Index
3. hstore in PostgreSQL
4. Array in PostgreSQL

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