Friendly syntax

FeatureQL extends standard SQL with features that make queries more readable and maintainable:

Automatic Dependency Resolution

The query engine automatically resolves dependencies, so you can reference columns before they're defined.

Alternative Assignment Syntax

For better readability, you can reverse expr AS identifier using := or IS.

expr AS identifier can then be written:

• identifier := expr
• identifier IS expr

Function Chaining

Function chaining allows you to write nested functions in a more readable, left-to-right format. Instead of writing nested functions like FUNC1(FUNC2(X)), you can express them as X.FUNC2().FUNC1().

When using function chaining:

• The expression before the dot (.) becomes the first argument of the function
• For functions with multiple arguments, provide the remaining arguments within the parentheses
• Use parentheses () to control precedence, especially with type casting operations

Key insights from the chaining examples:

• Simple chaining: (1+2).MULTIPLY(3) is equivalent to MULTIPLY((1+2), 3)
• Multiple operations: (1).ADD(2).MULTIPLY(3) chains left-to-right: first add 2 to 1, then multiply by 3
• Type casting precedence: (1).ADD(2).MULTIPLY(3)::(DOUBLE).SQRT()::BIGINT shows how parentheses control casting scope
• String operations: .TRIM().LOWER() chains naturally for text processing

This chainable syntax enhances code readability by making the sequence of operations more intuitive and easier to follow.

Advanced chaining with namespaces

When working with namespaced features and functions, chaining syntax requires careful attention to disambiguation:

Important distinctions:

• Quoted names: "FM.MYFEATURES.FEATURE1".ADD(1) treats the entire quoted string as a feature name
• Namespaced features: FM.MYFEATURES.FEATURE1.ADD(1) chains the ADD function on the namespaced feature
• Parentheses for clarity: (FEATURE1).ADD(2) explicitly marks the feature boundary
• Function quoting: (FEATURE1)."ADD"(3) calls the ADD function explicitly

Use parentheses and quotes strategically to ensure FeatureQL interprets your chaining intentions correctly.

Flexible Formatting

Trailing commas are supported and whitespace and formatting are flexible.

This makes it easier to:

• Reorder columns without breaking syntax
• Write more maintainable queries

Functions aliases

SQL dialects have different names for the same operation. FeatureQL accepts function aliases to provide flexibility and accommodate users coming from different SQL dialects.

Common alias patterns include:

• Complex structure types: ARRAY/LIST, ROW/STRUCT
• Construction syntax: ARRAY[...] and ARRAY(...), ROW(...) and ROW[...]
• Type-specific naming: SLICE(), LIST_SLICE(), and ARRAY_SLICE()
• Mathematical functions with full and abbreviated forms: POWER() and POW()

You can use any alias when writing your feature definition, but FeatureQL converts them to a single canonical function name when saved. This lets you use function names that match your backend's native syntax while ensuring consistency in stored feature definitions.

Intermediate features using WITH

When writing complex queries, you often need intermediate features that you don't want to expose in your final output.

You can use the WITH clause to keep these calculations private while only exposing the final results you want to show.

In this example, NUMBER2 is used in calculations but not exposed in the final output, while NUMBER1 and NUMBER3 are visible in the results.

Benefits of this approach:

• Maintains named intermediate features for clarity
• Helps separate logic from presentation
• Keeps your query output clean and focused

Note: Features corresponding to "internal" functions cannot be returned and therefore must then be defined in the WITH clause.

Function type	Why it can't be returned	What to return instead
INPUT()	Returns input placeholder	Return the BIND_XXX() binding values to the input
ENTITY()	Returns entity	Return the BIND_XXX() binding values to the INPUT() that references the entity
SOURCE_XXX()	Returns source	Return the EXTERNAL_XXX() using the source as parameters
UDF() and MACRO()	Returns function	Return the UDF() or MACRO() applied to some parameters