The script performs a LEFT JOIN operation, joining Table.B to the existing Table.A based on the common key field, ID.

1. Keep all rows from the left table: A LEFT JOIN retains all original rows from the left table (Table.A).

2. Match and update: It then looks for matching ID values in the right table (Table.B). For the matching key ID=3, the data from Table.B is joined. Since the non-key field Value has the same name in both tables, the value from Table.B ('X') updates/overwrites the original value in Table.A ('C').

3. Discard non-matching right-table rows: Rows from Table.B with IDs that do not exist in Table.A (ID=4 and ID=5) are discarded.

The final Table.A contains all its original keys, with the data for the matching key updated.

A: This result represents a FULL OUTER JOIN or CONCATENATE operation, as it includes all rows from both tables, which is incorrect for a LEFT JOIN.

B: This result incorrectly creates a duplicate row for the matching key ID=3. A Qlik JOIN updates the existing row, it does not add a new one for the same key.

C: This result shows only the single row where the keys matched, which is the behavior of an INNER JOIN, not a LEFT JOIN.

1. Qlik Sense for Windows Help: In the section on data loading script syntax, the Join prefix is detailed. It specifies that a LEFT JOIN includes all rows from the first table and only matching rows from the second. The examples implicitly demonstrate that for matching keys, values in identically named non-key fields are updated from the second table.

Source: Qlik Sense on Windows Help, "Scripting" -> "Script syntax and chart functions" -> "Script regular statements" -> "Join".

2. Qlik Community Technical Brief: While not a formal publication, technical articles by Qlik employees often clarify these behaviors. The logic of a LEFT JOIN is to keep the entire left table and enrich it with data from the right table where keys match. If non-key field names are identical, the join acts as an update for the matched records.

Source: Qlik Community, "Technical Brief: Joins and Lookups", which explains the fundamental difference between Qlik's associative logic and traditional SQL joins, including the update-like behavior on matching keys.