Left Join left-join

Performs a left join between two tables, keeping all rows from the left table and matching rows from the right table.

;; Create sample tables
↪ (set x (table [a b c d] 
    (list (list "aaaaaa" "bbbbbbbbbb" "cc" "dd")
          ['I 'J 'K 'I] 
          [0 1 2 3]
          [0 1 2 3])))

↪ (set y (table [a b c d e] 
    (list (list "aa" "bb" "cc" "dd" "ee")
          ['I 'J 'K 'I 'J]
          [0 1 2 3 4]
          [0 1 2 3 4]
          [0 1 2 3 4])))

;; Left join on single column
↪ (left-join [a] x y)
┌────────────┬───┬───┬───┬─────┐
│ a          │ b │ c │ d │ e   │
├────────────┼───┼───┼───┼─────┤
│ aaaaaa     │ I │ 0 │ 0 │ null│
│ bbbbbbbbbb │ J │ 1 │ 1 │ null│
│ cc         │ K │ 2 │ 2 │ 2   │
│ dd         │ I │ 3 │ 3 │ 3   │
└────────────┴───┴───┴───┴─────┘

;; Left join on multiple columns
↪ (left-join [a b] x y)
┌────────────┬───┬───┬───┬─────┐
│ a          │ b │ c │ d │ e   │
├────────────┼───┼───┼───┼─────┤
│ aaaaaa     │ I │ 0 │ 0 │ null│
│ bbbbbbbbbb │ J │ 1 │ 1 │ null│
│ cc         │ K │ 2 │ 2 │ 2   │
│ dd         │ I │ 3 │ 3 │ null│
└────────────┴───┴───┴───┴─────┘

Syntax

(left-join columns left-table right-table)

- columns: Vector of column names to join on - left-table: First table to join (all rows preserved) - right-table: Second table to join (matching rows only)

Note

• Keeps all rows from left table
• Fills missing matches with null
• Column names from both tables are preserved
• Join columns must exist in both tables
• Can join on multiple columns by providing a vector of column names

Tip

Use left join when you want to keep all rows from the first table, even if they don't have matches