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Documentation Index

Fetch the complete documentation index at: https://mintlify.com/questdb/questdb/llms.txt

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QuestDB provides a comprehensive set of SQL functions organized by category. All functions are implemented in zero-GC Java for high performance.

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Function Categories

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Date and Time Functions

Manipulate timestamps, dates, and time intervals. QuestDB supports microsecond and nanosecond precision. View Date/Time Functions Key functions:
  • now() - Current timestamp
  • date_trunc() - Truncate timestamp to specified unit
  • year(), month(), day() - Extract date parts
  • timestamp_floor() - Floor timestamp to interval
  • dateadd() - Add interval to timestamp

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Aggregation Functions

Compute aggregate values across rows in GROUP BY queries. View Aggregation Functions Key functions:
  • count() - Count rows
  • sum(), avg() - Sum and average
  • min(), max() - Minimum and maximum
  • stddev(), variance() - Statistical functions
  • string_agg() - Concatenate strings

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String Functions

Manipulate string, varchar, and symbol types. View String Functions Key functions:
  • concat() - Concatenate values
  • length() - String length
  • upper(), lower() - Case conversion
  • substring() - Extract substring
  • replace() - Replace text

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Numeric Functions

Mathematical operations and transformations. View Numeric Functions Key functions:
  • abs(), sign() - Absolute value and sign
  • round(), ceil(), floor() - Rounding
  • sqrt(), pow() - Power functions
  • sin(), cos(), tan() - Trigonometry

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Finance Functions

Specialized functions for orderbook and market data analysis. View Finance Functions Key functions:
  • mid() - Mid price calculation
  • spread() - Bid-ask spread
  • vwap() - Volume-weighted average price
  • twap() - Time-weighted average price

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Function Signatures

Function signatures in QuestDB use type notation:
  • D - DOUBLE
  • I - INT
  • L - LONG
  • S - STRING
  • N - TIMESTAMP (any precision)
  • V - Variable arguments
  • s - STRING constant

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Example

round(DI)
This signature means round() takes a DOUBLE and an INT parameter.

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NULL Handling

Most functions return NULL when any input is NULL. Exceptions are documented in individual function references.

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Performance Considerations

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SIMD Acceleration

Many aggregation functions use SIMD instructions for vectorized computation:
  • sum(), avg(), min(), max()
  • Statistical functions like stddev(), variance()

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Constant Folding

The query optimizer evaluates constant expressions at compile time: 
-- Evaluated once at compile time
SELECT * FROM trades WHERE price > 100.0 * 1.05;

-- Evaluated for each row
SELECT * FROM trades WHERE price > base_price * 1.05;

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Runtime Constants

Functions like now() are evaluated once per query execution, not per row: 
-- now() called once, not for each row
SELECT * FROM trades WHERE timestamp > now() - INTERVAL '1' HOUR;

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Type Casting

QuestDB supports explicit type casting with :: syntax: 
SELECT 
    '123'::INT,
    456::STRING,
    '2024-01-01'::TIMESTAMP
FROM trades;
Many functions perform implicit casting when safe.

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See Also