Parameters and LET

PARAM dias   INT DEFAULT 7;              -- batch: -p dias=3 | http: query string
PARAM desde  TIMESTAMP;                  -- no default = required
PARAM job    JSON FROM BODY;             -- whole JSON body as a document
PARAM tenant STRING FROM HEADER('X-Tenant');

• Reference with $: $dias, $desde. JSON documents navigate by dotted path — $job.tables, $job.source.host — resolved to literals at plan time. A JSON param takes its document from -p job='{"a":1}' (or a kernel’s params), else the request body in HTTP mode, else a string DEFAULT; a path to a key the document lacks is an error naming the key. check with no value bound reads every path as null.
• Safe navigation: $job.filtro?.uf — a missing intermediate resolves the whole path to null instead of erroring.
• Types: BOOL INT FLOAT STRING BYTES DATE TIME TIMESTAMP DECIMAL(p,s) JSON (common synonyms accepted: INTEGER BIGINT DOUBLE TEXT VARCHAR(n) DATETIME NUMERIC ...). A value bound from text — -p, a kernel’s params, a default — is read as a CAST reads it and keeps the declared type: -p d=2026-02-01 is a DATE (date_add('day', 1, $d) works), a date alone bound to a TIMESTAMP is its midnight, TIME takes HH:MM[:SS[.ffffff]], and a DECIMAL(10,2) rounds 12.345 to 12.35. Text that is not one fails the run, and check, naming the param and the value. DECIMAL alone is DECIMAL(38,0); DECIMAL(p) without a scale is refused.
• Source defaults: scalars bind from the query string, JSON from the body. A query-string value is decoded as a browser or a form encodes it: %C3%A3 is ã, + is a space and %2B a plus. FROM QUERY, FROM BODY and FROM HEADER('X-Name') say so explicitly; a bare FROM HEADER reads the header named like the param.

LET name = <expr>; is PARAM’s sealed sibling: a script-scoped constant folded once at plan time (in declaration order; it may reference $params and earlier $lets) and referenced as $name. It can never be bound externally — -p name=... is an error, HTTP binding ignores it, and it is not part of an endpoint’s parameter surface. A LET and a PARAM may not share a name. LET run_ts = now(); gives one consistent timestamp across every pipeline of a run.

LET name = (SELECT ...); binds the single cell of a query instead, run when the statement is reached (so it may read anything the script can) — see Subqueries. An expression LET cannot reference a query LET: expression LETs fold before any query runs.