Mutations

These are the primitive write verbs; the MySQL-style shorthands desugar to loops built from these.

SET — write an attribute

FOREACH office IN office
    WHERE office.id = 216000
    SET office.name = "New Office Name"
    BREAK;
;

SET v.attr = <expr> always overwrites, unconditionally.

MERGE — write only if missing (idempotent)

; add an attribute only where missing — existing values win, even different ones
FOREACH arm IN arms
    MERGE arm.tier = 1
;

MERGE v.attr = <expr> is the idempotent counterpart to SET: if the attribute already has a value, that value wins — even if it differs from what you're merging in. Safe to re-run.

DELETE — remove an attribute or element

DELETE IGNORE arm.unlock_civi_science;   attribute; IGNORE: no error if absent
DELETE arm;                              the current element itself
DELETE GROUP legacy_stuff;                the whole group container
DELETE TAG Obsolete;                      every <Obsolete> element, any depth

Without IGNORE, deleting something that doesn't exist is an error. IGNORE suppresses it.

REPLACE GROUP — wholesale replacement

REPLACE GROUP new_continued_cost
RAW XML `
<ItemSpec id="52034301" level="1" cost="500"/>
<ItemSpec id="52034302" level="2" cost="1000"/>
`;

Replaces the group's children entirely with the parsed fragment.

INSERT INTO GROUP — append

INSERT INTO GROUP goods RAW XML `<ItemSpec id="999"/>`;

Appends the fragment's elements to the group, alongside whatever's already there.

MERGE INTO GROUP — upsert

; upsert (idempotent): match children by id (then name, then tag);
; matched -> cited attributes updated, the rest preserved; no match -> inserted
MERGE INTO GROUP goods
RAW XML `
<ItemSpec id="52034301" cost="600"/>
<ItemSpec id="52034999" level="9" cost="9000"/>
`;

For each element in the fragment, MERGE INTO GROUP looks for an existing child matching by id, then name, then tag:

• Matched — only the attributes present in the fragment are updated; everything else on the existing element is preserved. If the fragment element has children of its own, they replace the existing children.
• Unmatched — the fragment element is inserted as a new child.

This makes MERGE INTO GROUP the safe, re-runnable way to apply a batch of "these attributes, if they differ" updates without clobbering fields you didn't mention.

RAW XML fragments

RAW XML \...`is a backtick-delimited raw fragment, parsed as XML and used byREPLACE, INSERT INTO, and MERGE INTO`. It can contain multiple sibling elements.