> ## Documentation Index
> Fetch the complete documentation index at: https://dune-tables-docs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Conditional expressions

### CASE

The standard SQL `CASE` expression has two forms. The "simple" form
searches each `value` expression from left to right until it finds one
that equals `expression`:

```text
CASE expression
    WHEN value THEN result
    [ WHEN ... ]
    [ ELSE result ]
END
```

The `result` for the matching `value` is returned. If no match is found,
the `result` from the `ELSE` clause is returned if it exists, otherwise
null is returned. Example:

```sql
    SELECT a,
           CASE a
               WHEN 1 THEN 'one'
               WHEN 2 THEN 'two'
               ELSE 'many'
           END
```

The "searched" form evaluates each boolean `condition` from left to
right until one is true and returns the matching `result`:

```text
CASE
    WHEN condition THEN result
    [ WHEN ... ]
    [ ELSE result ]
END
```

If no conditions are true, the `result` from the `ELSE` clause is
returned if it exists, otherwise null is returned. Example:

```sql
    SELECT a, b,
           CASE
               WHEN a = 1 THEN 'aaa'
               WHEN b = 2 THEN 'bbb'
               ELSE 'ccc'
           END
```

### IF

The `IF` expression has two forms, one supplying only a `true_value` and
the other supplying both a `true_value` and a `false_value`:

**`if(condition, true_value)`**

Evaluates and returns `true_value` if `condition` is true, otherwise
null is returned and `true_value` is not evaluated.

**`if(condition, true_value, false_value)`**

Evaluates and returns `true_value` if `condition` is true, otherwise
evaluates and returns `false_value`.

The following `IF` and `CASE` expressions are equivalent:

```sql
SELECT
  orderkey,
  totalprice,
  IF(totalprice >= 150000, 'High Value', 'Low Value')
FROM tpch.sf1.orders;
```

```sql
SELECT
  orderkey,
  totalprice,
  CASE
    WHEN totalprice >= 150000 THEN 'High Value'
    ELSE 'Low Value'
  END
FROM tpch.sf1.orders;
```

<h3 id="coalesce\_function">
  COALESCE \\
</h3>

**`coalesce(value1, value2\[, \...\])`**

Returns the f non-null `value` in the argument list. Like a `CASE`
expression, arguments are only evaluated if necessary.

### NULLIF

**`nullif(value1, value2)`**

Returns null if `value1` equals `value2`, otherwise returns `value1`.

### TRY

**`try(expression)`**

Evaluate an expression and handle certain types of errors by returning
`NULL`.

In cases where it is preferable that queries produce `NULL` or default
values instead of failing when corrupt or invalid data is encountered,
the `TRY` function may be useful. To specify default values, the `TRY`
function can be used in conjunction with the `COALESCE` function.

The following errors are handled by `TRY`:

* Division by zero
* Invalid cast or function argument
* Numeric value out of range

**`Examples`**

Source table with some invalid data:

```sql
SELECT * FROM shipping;
```

```text
origin_state | origin_zip | packages | total_cost
--------------+------------+----------+------------
California   |      94131 |       25 |        100
California   |      P332a |        5 |         72
California   |      94025 |        0 |        155
New Jersey   |      08544 |      225 |        490
(4 rows)
```

Query failure without `TRY`:

```sql
SELECT CAST(origin_zip AS BIGINT) FROM shipping;
```

```text
Query failed: Cannot cast 'P332a' to BIGINT
```

`NULL` values with `TRY`:

```sql
SELECT TRY(CAST(origin_zip AS BIGINT)) FROM shipping;
```

```text
origin_zip
------------
     94131
     NULL
     94025
     08544
(4 rows)
```

Query failure without `TRY`:

```sql
SELECT total_cost / packages AS per_package FROM shipping;
```

```text
Query failed: Division by zero
```

Default values with `TRY` and `COALESCE`:

```sql
SELECT COALESCE(TRY(total_cost / packages), 0) AS per_package FROM shipping;
```

```text
per_package
-------------
         4
        14
         0
        19
(4 rows)
```