Transformers

Transformers modify column values before they are compared in queries or emitted in SQL. They use the pipe (|) syntax, applied left-to-right.

Pipe Syntax

Apply a transformer to a column with |:

message|upper = "ERROR"

This transforms the value of message using upper before comparing with "ERROR".

Chaining

Chain multiple transformers with additional pipes:

message|lower|len > 100

Transformers apply left-to-right: lower runs first (string to string), then len (string to int). The result is compared with > 100.

Type System

Each transformer declares an input type and output type. Chained transformers must be type-compatible — the output type of one must match the input type of the next.

Type	Description
string	Text values
int	Integer numbers
float	Floating-point numbers
bool	Boolean values
array	Array of values (use has operator to check membership)

Built-in Transformers

Transformer	Input	Output	Description
upper	string	string	Convert to uppercase
lower	string	string	Convert to lowercase
len	string	int	Get string length
split	string	array	Split by delimiter: split(".")

SQL Output by Dialect

Transformers generate dialect-specific SQL function calls. Chained transformers produce nested calls (innermost first):

Single transformer: status|upper = "ERROR"

Dialect	Generated SQL
ClickHouse	equals(upper(status), 'ERROR')
PostgreSQL	UPPER(status) = 'ERROR'
StarRocks	UPPER(\status`) = ‘ERROR’`

Chained transformers: message|lower|len > 100

Dialect	Generated SQL
ClickHouse	length(lower(message)) > 100
PostgreSQL	LENGTH(LOWER(message)) > 100
StarRocks	LENGTH(LOWER(\message`)) > 100`

Split with has: message|split(" ") has "hello"

Dialect	Generated SQL
ClickHouse	has(splitByChar(' ', message), 'hello')
PostgreSQL	'hello' = ANY(STRING_TO_ARRAY(message, ' '))
StarRocks	array_contains(SPLIT(`message`, ' '), 'hello')

Type Errors

If a chain has incompatible types, the editor shows an error:

message|len|upper

This fails because len outputs int, but upper requires string input. The editor displays: “len outputs int, upper requires string input”.

Examples

status|upper = "ERROR"

message|lower|len > 100

host|lower != "localhost"

path|len > 0

tags|split(",") has "urgent"

Transformers vs. Renderers

Transformers run before the alias and change the value flyql emits in SQL or matches against. Renderers run after the alias and attach display metadata without ever affecting the generated SQL or the matcher result. If you want to say “return this value uppercased”, use a transformer. If you want to say “render this column as a clickable link in my app”, use a renderer.

Concern	Transformer	Renderer
Position in syntax	before alias	after alias
Affects generated SQL	yes	no
Affects matcher output	yes	no
Default registry	4 built-ins	empty

See Renderers for the post-alias pipe syntax and Custom Renderers for the registration API.