[WIP] Implement LET clause similar to OrientDB

src/39dojoin.js

@@ -7,12 +7,51 @@ function doJoin(query, scope, h) {
 	if (h >= query.sources.length) {
 		// Todo: check if this runs once too many
 		// Then apply where and select
-		if (query.wherefn(scope, query.params, alasql)) {
-			// If there is a GROUP BY then pipe to grouping function
-			if (query.groupfn) {
-				query.groupfn(scope, query.params, alasql);
-			} else {
-				query.data.push(query.selectfn(scope, query.params, alasql));
+		var params = query.params;
+		var originalParams = params;
+		var restoreQueryParams = false;
+		var previousValues;
+		if (query.lets && query.lets.length > 0) {
+			if (!params || typeof params !== 'object') {
+				params = {};
+				query.params = params;
+				restoreQueryParams = true;
+			}
+			previousValues = new Array(query.lets.length);
+			for (var i = 0; i < query.lets.length; i++) {
+				var assignment = query.lets[i];
+				var target = assignment.method === '@' ? alasql.vars : params;
+				previousValues[i] = {
+					target: target,
+					variable: assignment.variable,
+					exists: Object.prototype.hasOwnProperty.call(target, assignment.variable),
+					value: target[assignment.variable],
+				};
+				target[assignment.variable] = assignment.valuefn(scope, params, alasql);
+			}
+		}
+		try {
+			if (query.wherefn(scope, params, alasql)) {
+				// If there is a GROUP BY then pipe to grouping function
+				if (query.groupfn) {
+					query.groupfn(scope, params, alasql);
+				} else {
+					query.data.push(query.selectfn(scope, params, alasql));
+				}
+			}
+		} finally {
+			if (previousValues) {
+				for (var j = previousValues.length - 1; j >= 0; j--) {
+					var previous = previousValues[j];
+					if (previous.exists) {
+						previous.target[previous.variable] = previous.value;
+					} else {
+						delete previous.target[previous.variable];
+					}
+				}
+			}
+			if (restoreQueryParams) {
+				query.params = originalParams;
 			}
 		}
 	} else if (query.sources[h].applyselect) {

src/40select.js

@@ -12,6 +12,10 @@
 
 /* global yy */
 
+function formatLetExpression(assignment) {
+	return assignment.method + assignment.variable + ' = ' + assignment.expression.toString();
+}
+
 yy.Select = class Select {
 	constructor(params) {
 		Object.assign(this, params);
@@ -90,6 +94,9 @@ yy.Select = class Select {
 				})
 				.join('');
 		}
+		if (this.let && this.let.length > 0) {
+			s += ' LET ' + this.let.map(formatLetExpression).join(', ');
+		}
 		if (this.where) {
 			s += ' WHERE ' + this.where.toString();
 		}
@@ -183,6 +190,9 @@ yy.Select = class Select {
 			this.compileJoins(query);
 		}
 
+		// 2.5 Compile LET clause
+		this.compileLet(query);
+
 		// todo?: 3. Compile SELECT clause
 		// For ROWNUM()
 		query.rownums = [];
@@ -623,6 +633,19 @@ yy.Select = class Select {
 			}
 		});
 	}
+
+	compileLet(query) {
+		if (!this.let || this.let.length === 0) return;
+
+		query.lets = this.let.map(assignment => ({
+			method: assignment.method,
+			variable: assignment.variable,
+			valuefn: new Function(
+				'p,params,alasql',
+				'var y;return ' + assignment.expression.toJS('p', query.defaultTableid, query.defcols)
+			),
+		}));
+	}
 };
 
 /**

src/alasqlparser.jison

@@ -533,11 +533,11 @@ WithTable
 /* SELECT */
 
 Select
-	: SelectClause RemoveClause? IntoClause FromClause PivotClause? WhereClause GroupClause  UnionClause OrderClause LimitClause
+	: SelectClause RemoveClause? IntoClause FromClause PivotClause? LetClause WhereClause GroupClause  UnionClause OrderClause LimitClause
 		{
 			yy.extend($$,$1); yy.extend($$,$2); yy.extend($$,$3); yy.extend($$,$4);
 		    yy.extend($$,$5); yy.extend($$,$6);yy.extend($$,$7);
-		    yy.extend($$,$8); yy.extend($$,$9); yy.extend($$,$10);
+		    yy.extend($$,$8); yy.extend($$,$9); yy.extend($$,$10); yy.extend($$,$11);
 		    $$ = $1;
 		    if(yy.exists) $$.exists = yy.exists.slice();
 /*		    if(yy.queries) $$.queries = yy.queries;
@@ -572,10 +572,10 @@ ParenthesizedSelect
 	;
 
 SelectWithoutOrderOrLimit
-	: SelectClause RemoveClause? IntoClause FromClause PivotClause? WhereClause GroupClause UnionClause
+	: SelectClause RemoveClause? IntoClause FromClause PivotClause? LetClause WhereClause GroupClause UnionClause
 		{
 			yy.extend($$,$1); yy.extend($$,$2); yy.extend($$,$3); yy.extend($$,$4);
-		    yy.extend($$,$5); yy.extend($$,$6);yy.extend($$,$7);yy.extend($$,$8);
+		    yy.extend($$,$5); yy.extend($$,$6);yy.extend($$,$7);yy.extend($$,$8);yy.extend($$,$9);
 		    $$ = $1;
 		    if(yy.exists) $$.exists = yy.exists.slice();
 		}
@@ -1096,6 +1096,24 @@ WhereClause
 		{ $$ = {where: new yy.Expression({expression:$2})}; }
 	;
 
+LetClause
+	: { $$ = undefined; }
+	| LET LetExpressionsList
+		{ $$ = {let: $2}; }
+	;
+
+LetExpressionsList
+	: LetExpression
+		{ $$ = [$1]; }
+	| LetExpressionsList COMMA LetExpression
+		{ $1.push($3); $$ = $1; }
+	;
+
+LetExpression
+	: AtDollar Literal EQ Expression
+		{ $$ = new yy.SetVariable({variable:$2, expression:$4, method:$1});}
+	;
+
 GroupClause
 	: { $$ = undefined; }
 	| GROUP BY GroupExpressionsList HavingClause