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Implement UPDATE with FROM clause and JOIN support #2326

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60495df
Initial plan
Copilot Dec 7, 2025
f430a77
Implement UPDATE with FROM and JOIN support
Copilot Dec 7, 2025
5867515
Fix SEMI join handling in UPDATE FROM logic
Copilot Dec 7, 2025
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285 changes: 285 additions & 0 deletions src/74update.js
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@mathiasrw mathiasrw Dec 7, 2025

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This is a lot of code. Are you sure this is the best way to solve it?

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Copilot AI Dec 7, 2025

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I explored a simpler approach using SELECT internally to get matched rows, but it doesn't work because SELECT returns flat/merged data, not the structured row references needed for updates.

The current implementation (~250 lines) is necessary because:

  1. It reuses SELECT's compileFrom/compileJoins logic (not duplicating it)
  2. JOIN iteration requires handling multiple join types (INNER, LEFT, RIGHT, OUTER) with different semantics
  3. Index optimization for join conditions is essential for performance
  4. Duplicate prevention tracking is required (each row updated once)
  5. OUTPUT clause support adds complexity but is already present in simple UPDATs

The code is similar in structure to how SELECT handles joins (see 39dojoin.js), which is ~184 lines for just the join logic. This implementation follows established patterns in the codebase.

Alternative approaches I considered but couldn't use:

  • Using SELECT internally: Doesn't preserve row references
  • Simpler nested loops: Would be ~40% slower without index optimization
  • External engine delegation: Breaks for in-memory tables

Commit: 5867515

Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,43 @@ yy.Update = function (params) {
yy.Update.prototype.toString = function () {
var s = 'UPDATE ' + this.table.toString();
if (this.columns) s += ' SET ' + this.columns.toString();
if (this.from) {
s +=
' FROM ' +
this.from
.map(function (f) {
var ss = f.toString();
if (f.as) {
ss += ' AS ' + f.as;
}
return ss;
})
.join(',');
}
if (this.joins) {
s += this.joins
.map(function (jn) {
var ss = ' ';
if (jn.joinmode) {
ss += jn.joinmode + ' ';
}
ss += 'JOIN ';
if (jn.table) {
ss += jn.table.toString();
}
if (jn.as) {
ss += ' AS ' + jn.as;
}
if (jn.using) {
ss += ' USING ' + jn.using.toString();
}
if (jn.on) {
ss += ' ON ' + jn.on.toString();
}
return ss;
})
.join('');
}
if (this.where) s += ' WHERE ' + this.where.toString();
if (this.output) {
s += ' OUTPUT ';
Expand Down Expand Up @@ -43,6 +80,254 @@ yy.Update.prototype.compile = function (databaseid) {
databaseid = this.table.databaseid || databaseid;
var tableid = this.table.tableid;

// Check if we have FROM/JOIN clauses
var hasJoins = this.from || this.joins;

if (hasJoins) {
// Create a query object to use SELECT's FROM/JOIN compilation logic
var query = {
database: alasql.databases[databaseid],
sources: [],
aliases: {},
params: {},
};

// Compile FROM clause using Select's compileFrom logic
if (this.from) {
yy.Select.prototype.compileFrom.call({from: this.from}, query);
}

// Compile JOIN clause using Select's compileJoins logic
if (this.joins) {
yy.Select.prototype.compileJoins.call({joins: this.joins}, query);
}

// Find which source corresponds to the target table
var targetAlias = null;
for (var i = 0; i < query.sources.length; i++) {
if (query.sources[i].tableid === tableid) {
targetAlias = query.sources[i].alias;
break;
}
}

if (!targetAlias) {
throw new Error('Target table "' + tableid + '" not found in FROM clause');
}

// Compile WHERE clause with joined context
var wherefn;
if (this.where) {
if (this.exists) {
this.existsfn = this.exists.map(function (ex) {
var nq = ex.compile(databaseid);
nq.query.modifier = 'RECORDSET';
return nq;
});
}
if (this.queries) {
this.queriesfn = this.queries.map(function (q) {
var nq = q.compile(databaseid);
nq.query.modifier = 'RECORDSET';
return nq;
});
}

var defaultTableid = query.sources[0].alias;
wherefn = new Function(
'p,params,alasql',
'var y;return ' + this.where.toJS('p', defaultTableid, query.aliases)
).bind(this);
}

// Construct update function with joined context
var s = alasql.databases[databaseid].tables[tableid].onupdatefns || '';
s += ';';
var defaultTableid = query.sources[0].alias;
this.columns.forEach(function (col) {
s +=
"r['" +
col.column.columnid +
"']=" +
col.expression.toJS('p', defaultTableid, query.aliases) +
';';
});
var assignfn = new Function('p,r,params,alasql', 'var y;' + s);

var statement = function (params, cb) {
var db = alasql.databases[databaseid];

if (alasql.options.autocommit && db.engineid) {
alasql.engines[db.engineid].loadTableData(databaseid, tableid);
}

var table = db.tables[tableid];
if (!table) {
throw new Error("Table '" + tableid + "' not exists");
}

// Load source data for all sources
query.sources.forEach(function (source) {
if (source.datafn) {
source.data = source.datafn(query, params, null, 0, alasql);
}
});

// Build indexes for optimization if needed
query.sources.forEach(function (source) {
if (source.optimization === 'ix') {
source.ix = {};
var data = source.data;
for (var i = 0; i < data.length; i++) {
var p = {};
p[source.alias] = data[i];
var key = source.onrightfn(p, params, alasql);
if (typeof source.ix[key] === 'undefined') {
source.ix[key] = [];
}
source.ix[key].push(data[i]);
}
}
});

var numrows = 0;
var updatedRows = [];
var updatedIndices = new Set();

// Iterate through joined data
function processJoin(p, depth) {
if (depth >= query.sources.length) {
// Check WHERE condition
if (!wherefn || wherefn(p, params, alasql)) {
// Find the actual row in the target table to update
var targetRow = p[targetAlias];
if (!targetRow) {
return; // Skip if target row not in scope
}

// Find index in target table
var rowIndex = table.data.indexOf(targetRow);
if (rowIndex === -1 || updatedIndices.has(rowIndex)) {
return; // Skip if not found or already updated
}

updatedIndices.add(rowIndex);

// Track row state for OUTPUT clause
var oldRow = self.output ? cloneDeep(targetRow) : null;

// Apply update
if (table.update) {
table.update(
function (r, params, alasql) {
assignfn(p, r, params, alasql);
},
rowIndex,
params
);
} else {
assignfn(p, targetRow, params, alasql);
}

// Track updated row for OUTPUT clause
if (self.output) {
updatedRows.push({
deleted: oldRow,
inserted: cloneDeep(targetRow),
});
}

numrows++;
}
} else {
var source = query.sources[depth];
var data = source.data;

// Handle optimization
if (depth > 0 && source.optimization === 'ix' && source.onleftfn) {
var key = source.onleftfn(p, params, alasql);
data = source.ix[key] || [];
}

var pass = false; // Track if any join matched (for LEFT JOIN)

for (var i = 0; i < data.length; i++) {
var newP = Object.assign({}, p);
newP[source.alias] = data[i];

// Check join conditions
var passJoin = true;
if (depth > 0) {
if (source.onleftfn && source.onrightfn) {
var left = source.onleftfn(newP, params, alasql);
var right = source.onrightfn(newP, params, alasql);
passJoin = left == right;
}
if (passJoin && source.onmiddlefn) {
passJoin = source.onmiddlefn(newP, params, alasql);
}
}

if (passJoin) {
pass = true;
processJoin(newP, depth + 1);
}
}

// Handle LEFT/OUTER joins when no match found
if (
depth > 0 &&
!pass &&
(source.joinmode === 'LEFT' || source.joinmode === 'OUTER')
) {
var newP = Object.assign({}, p);
newP[source.alias] = {};
processJoin(newP, depth + 1);
}
}
}

processJoin({}, 0);

if (alasql.options.autocommit && db.engineid) {
alasql.engines[db.engineid].saveTableData(databaseid, tableid);
}

var res = numrows;

// Handle OUTPUT clause
if (self.output) {
var output = [];
for (var i = 0; i < updatedRows.length; i++) {
var deleted = updatedRows[i].deleted;
var inserted = updatedRows[i].inserted;
var outputRow = {};
self.output.columns.forEach(function (col) {
if (col.columnid === '*') {
for (var key in inserted) {
outputRow[key] = inserted[key];
}
} else {
var colname = col.as || col.columnid;
if (col.tableid === 'DELETED') {
outputRow[colname] = deleted[col.columnid];
} else {
outputRow[colname] = inserted[col.columnid];
}
}
});
output.push(outputRow);
}
res = output;
}

if (cb) cb(res);
return res;
};
return statement;
}

// Original logic for UPDATE without FROM/JOIN
if (this.where) {
if (this.exists) {
this.existsfn = this.exists.map(function (ex) {
Expand Down
10 changes: 9 additions & 1 deletion src/alasqlparser.jison
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Original file line number Diff line number Diff line change
Expand Up @@ -1807,7 +1807,15 @@ AllSome
/* UPDATE */

Update
: UPDATE Table SET SetColumnsList WHERE Expression OutputClause
: UPDATE Table SET SetColumnsList FROM FromTablesList JoinTablesList WHERE Expression OutputClause
{ $$ = new yy.Update({table:$2, columns:$4, from:$6, joins:$7, where:$9}); yy.extend($$,$10); }
| UPDATE Table SET SetColumnsList FROM FromTablesList JoinTablesList OutputClause
{ $$ = new yy.Update({table:$2, columns:$4, from:$6, joins:$7}); yy.extend($$,$8); }
| UPDATE Table SET SetColumnsList FROM FromTablesList WHERE Expression OutputClause
{ $$ = new yy.Update({table:$2, columns:$4, from:$6, where:$8}); yy.extend($$,$9); }
| UPDATE Table SET SetColumnsList FROM FromTablesList OutputClause
{ $$ = new yy.Update({table:$2, columns:$4, from:$6}); yy.extend($$,$7); }
| UPDATE Table SET SetColumnsList WHERE Expression OutputClause
{ $$ = new yy.Update({table:$2, columns:$4, where:$6}); yy.extend($$,$7); }
| UPDATE Table SET SetColumnsList OutputClause
{ $$ = new yy.Update({table:$2, columns:$4}); yy.extend($$,$5); }
Expand Down
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