Used to combine multiple rows into a single string.

Example

item	transaction
3	1003
1	1001
2	1002

Query

SELECT
    tl.vendor_id,
    STRING_AGG(t.tranid::text, '; ' ORDER BY tl.item) AS lpb
FROM transaction_line tl
JOIN transactions t
    ON t.id = tl.transaction
GROUP BY tl.vendor_id;

Result

vendor_id	lpb
1	LPB-001; LPB-002
2	LPB-010; LPB-011

Aggregation Flow

Explanation

The query works by:

1. Joining transaction_line with transactions
2. Grouping data by vendor_id
3. Sorting rows using ORDER BY tl.item
4. Combining all transaction IDs into one string using STRING_AGG

SQL Equivalent Functions

Database	Function
PostgreSQL	STRING_AGG()
Oracle	LISTAGG()
MySQL	GROUP_CONCAT()
SQL Server	STRING_AGG()