Partial Implementation of aliasing functionality.

Author: axj2613

src/RelExpr.js

@@ -1,6 +1,7 @@
 // @flow
 import React, {useRef} from 'react';
 import {
+  Alias,
   UnaryRelOp,
   Projection,
   Rename,
@@ -97,6 +98,14 @@ const RelExpr: StatelessFunctionalComponent<Props> = (props) => {
       case 'relation':
         return <Relation name={expr.relation} />;
 
+      case 'alias':
+        return (
+          <Alias
+            value={expr.alias.value}
+            alias_value={expr.alias.alias_value}
+          />
+        );
+
       case 'order_by':
         return (
           <OrderBy

src/RelOp.js

@@ -137,6 +137,17 @@ export const Intersect: StatelessFunctionalComponent<{||}> = () => (
   <span>&cap;</span>
 );
 
+export const Alias: StatelessFunctionalComponent<{
+  value: string,
+  alias_value: string,
+}> = (props) => {
+  return (
+    <span>
+      &rho;<sub>{props.alias_value}</sub> {props.value}
+    </span>
+  );
+};
+
 export const OrderBy: StatelessFunctionalComponent<{
   columns: Array<OrderByColumn>,
   relation: Node,
@@ -146,7 +157,7 @@ export const OrderBy: StatelessFunctionalComponent<{
     .join(', ');
   return (
     <span>
-      τ<sub>{columnSort}</sub> {props.relation}
+      &tau;<sub>{columnSort}</sub> {props.relation}
     </span>
   );
 };

src/modules/data.js

@@ -5,6 +5,7 @@ import {produce} from 'immer';
 import department from '../resources/Department.json';
 import doctor from '../resources/Doctor.json';
 import patient from '../resources/Patient.json';
+import relation from '../Relation';
 
 export const CHANGE_EXPR = 'CHANGE_EXPR';
 export const RESET_EXPR = 'RESET_EXPR';
@@ -86,6 +87,29 @@ function getCombinedColumns(left: {[string]: any}, right: {[string]: any}) {
   return combinedColumns;
 }
 
+function getAliasedOutput(relation: {[string]: any}, alias: string) {
+  const newColumns: Array<string> = [];
+  const newData: Array<{[string]: any}> = [];
+  for (const column of relation.columns) {
+    const newColumnName = alias + '.' + column;
+    newColumns.push(newColumnName);
+  }
+  for (const datum of relation.data) {
+    let newDatum: {[string]: any} = {};
+    for (const column of relation.columns) {
+      newDatum[alias + '.' + column] = datum[column];
+    }
+    newData.push(newDatum);
+  }
+
+  const output: Output = {
+    name: alias,
+    columns: newColumns,
+    data: newData,
+  };
+  return output;
+}
+
 function getCombinedData(
   leftName: string,
   leftRow: {[string]: any},
@@ -327,6 +351,12 @@ function applyExpr(
       // Make a copy of the data from a source table and return it
       return {...sourceData[expr.relation]};
 
+    case 'alias':
+      return getAliasedOutput(
+        sourceData[expr.alias.value],
+        expr.alias.alias_value
+      );
+
     case 'order_by':
       let ordData = applyExpr(expr.order_by.children[0], sourceData);
 

src/modules/relexp.js

@@ -279,7 +279,6 @@ function convertExpr(
       }
 
     default:
-      console.log(expr);
       // Produce an error if the expression is unsupported
       throw new Error('Invalid expression.');
   }
@@ -396,9 +395,16 @@ function buildRelExp(
     case 'TableFactor':
       // Store this table as one referenced by the query
       tables.push(sql.value.value);
-
-      return {relation: sql.value.value};
-
+      if (sql.hasAs) {
+        return {
+          alias: {
+            value: sql.value.value,
+            alias_value: sql.alias.value,
+          },
+        };
+      } else {
+        return {relation: sql.value.value};
+      }
     case 'InnerCrossJoinTable':
       // Add the condition if it exists
       if (sql.condition) {

src/modules/relexp.test.js

@@ -47,6 +47,20 @@ it('converts a rename', () => {
   });
 });
 
+/** @test {relexp} */
+it('converts a aliasing operation', () => {
+  const sql = parser.parse('SELECT bar FROM foo as f');
+  const action = exprFromSql(sql.value, {foo: ['bar']});
+  expect(reducer({}, action)).toMatchObject({
+    expr: {
+      projection: {
+        arguments: {project: ['bar']},
+        children: [{alias: {alias_value: 'f', value: 'foo'}}],
+      },
+    },
+  });
+});
+
 /** @test {relexp} */
 it('converts a difference', () => {
   const sql = parser.parse('SELECT * FROM foo EXCEPT SELECT * FROM bar');