# `Selecto.SQL.Functions`

Advanced SQL function support for Selecto.

This module extends the existing function support in Selecto.Builder.Sql.Select
with additional advanced SQL functions including window functions, array operations,
string manipulation, and mathematical functions.

## Function Categories

### String Functions
- `substr/3` - Extract substring
- `trim/1`, `ltrim/1`, `rtrim/1` - String trimming
- `upper/1`, `lower/1` - Case conversion
- `length/1` - String length
- `position/2` - Find substring position
- `replace/3` - String replacement
- `split_part/3` - Split and extract part

### Mathematical Functions
- `abs/1` - Absolute value
- `ceil/1`, `floor/1` - Rounding functions
- `round/1`, `round/2` - Rounding with precision
- `power/2` - Exponentiation
- `sqrt/1` - Square root
- `mod/2` - Modulo operation
- `random/0` - Random number generation

### Date/Time Functions
- `now/0` - Current timestamp
- `date_trunc/2` - Truncate to date part
- `interval/1` - Time intervals
- `age/1`, `age/2` - Date arithmetic
- `date_part/2` - Enhanced extract functionality

### Array Functions
- `array_agg/1` - Array aggregation
- `array_length/1` - Array length
- `array_to_string/2` - Array to string conversion
- `string_to_array/2` - String to array conversion
- `unnest/1` - Array expansion
- `array_cat/2` - Array concatenation

### Window Functions
- `row_number/0` - Row numbering
- `rank/0` - Ranking with gaps
- `dense_rank/0` - Dense ranking
- `lag/1`, `lag/2` - Previous row values
- `lead/1`, `lead/2` - Next row values
- `first_value/1`, `last_value/1` - Window boundaries
- `ntile/1` - Percentile groups

### Conditional Functions
- Enhanced `case` expressions
- `decode/3+` - Oracle-style conditional
- `iif/3` - Simple if-then-else

## Usage Examples

    # String functions
    {:substr, "description", 1, 50}
    {:trim, "name"}
    {:upper, "category"}

    # Math functions
    {:round, "price", 2}
    {:power, "base", 2}

    # Window functions
    {:window, {:row_number}, over: [partition_by: ["category"], order_by: ["price"]]}
    {:window, {:lag, "price"}, over: [partition_by: ["product_id"], order_by: ["date"]]}

    # Array functions
    {:array_agg, "tag_name", over: [partition_by: ["product_id"]]}
    {:unnest, "tags"}

# `prep_advanced_selector`

Process advanced SQL functions that extend beyond the basic set.

This integrates with the existing prep_selector in Selecto.Builder.Sql.Select
to provide comprehensive function support.

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*Consult [api-reference.md](api-reference.md) for complete listing*