Query Language
An overview of the dbnl Query Language
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An overview of the dbnl Query Language
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The dbnl Query Language is a SQL-like language that allows for querying data in runs for the purpose of drawing visualizations, defining metrics or evaluating tests.
An expression is a combination of literals, values, operators, and functions. Expressions can evaluate to scalar or columnar values depending on their types and inputs. There are three types of expressions that can be composed into arbitrarily complex expressions.
Literal expressions are constant-valued expressions.
boolean
true
int
42
float
1.0
string
'hello world'
Column and scalar expressions are references to columns or scalar values in a run. They use dot-notation to reference a column or scalar within a run.
For example, a column named score in a run with id run_1234 can be referenced with the expression:
Function expressions are functions evaluated over zero or more other expressions. They make it possible to compose simple expressions into arbitrarily complex expressions.
For example, the word_count function can be used to compute the word count of the text column in a run with id run_1234 with the expression:
Operators are aliases for function expressions that enhance readability and ease of use. Operator precedence is the same as that of most SQL dialect.
Arithmetic operators
Arithmetic operators provide support for basic arithmetic operations.
-a
negate(a)
Negate an input.
a * b
multiply(a, b)
Multiply two inputs.
a / b
divide(a, b)
Divide two inputs.
a + b
add(a, b)
Add two inputs.
a - b
subtract(a, b)
Subtract two inputs.
Comparison operators
Comparison operators provide support for common comparison operations.
a = b
eq(a, b)
Equal to.
a != b
neq(a, b)
Not equal to.
a < b
lt(a, b)
Less than.
a <= b
lte(a, b)
Less than or equal to.
a > b
gt(a, b)
Greater than.
a >= b
gte(a, b)
Greater than or equal to
Logical operators
Logical operators provide support for boolean comparisons.
not b
not(a, b)
Logical not of input.
a and b
and(a, b)
Logical and of two inputs.
a or b
or(a, b)
Logical or of two inputs.
The dbnl Query Language follows the null semantics of most SQL dialect. With a few exception, when a null value is used as an input to a function or operator, the result is null.
4 > null
null
null = null
null
null + 2
null
word_count(null)
null
One exception to this is boolean functions and operators where ternary logic is used similar to most SQL dialects.
true
null
true
null
false
false
null
null
false
true
null
true
true
null
null
null
false
null
false
null
null
null
null
null
null
