Fix simple tabley sampling

lib/cartodb/utils/query-utils.js

@@ -89,9 +89,9 @@ module.exports.getQueryTopCategories = function(query, column, topN, includeNull
 };
 
 module.exports.getQuerySample = function(query, sampleProb, randomSeed = 0.5) {
-    const table = simpleQueryTable(query);
-    if (table) {
-        return getTableSample(table, sampleProb, randomSeed);
+    const singleTable = simpleQueryTable(query);
+    if (singleTable) {
+        return getTableSample(singleTable.table, singleTable.columns, sampleProb, randomSeed);
     }
     return `
         WITH __cdb_rndseed AS (
@@ -103,17 +103,17 @@ module.exports.getQuerySample = function(query, sampleProb, randomSeed = 0.5) {
     `;
 };
 
-function getTableSample(table, sampleProb, randomSeed) {
+function getTableSample(table, columns, sampleProb, randomSeed) {
     sampleProb *= 100;
     randomSeed *= Math.pow(2, 31) -1;
     return `
-        SELECT * FROM ${table} TABLESAMPLE BERNOULLI (${sampleProb}) REPEATABLE (${randomSeed})
+        SELECT ${columns} FROM ${table} TABLESAMPLE BERNOULLI (${sampleProb}) REPEATABLE (${randomSeed})
     `;
 }
 
 function simpleQueryTable(sql) {
     const basicQuery =
-        /\s*SELECT\s+[\*a-z0-9_,\s]+?\s+FROM\s+((\"[^"]+\"|[a-z0-9_]+)\.)?(\"[^"]+\"|[a-z0-9_]+)\s*;?\s*/i;
+        /\s*SELECT\s+([\*a-z0-9_,\s]+?)\s+FROM\s+((\"[^"]+\"|[a-z0-9_]+)\.)?(\"[^"]+\"|[a-z0-9_]+)\s*;?\s*/i;
     const unwrappedQuery = new RegExp("^"+basicQuery.source+"$", 'i');
     // queries for named maps are wrapped like this:
     var wrappedQuery = new RegExp(
@@ -127,9 +127,10 @@ function simpleQueryTable(sql) {
         match = sql.match(wrappedQuery);
     }
     if (match) {
-        const schema = match[2];
-        const table  = match[3];
-        return schema ? `${schema}.${table}` : table;
+        const columns = match[1];
+        const schema = match[3];
+        const table  = match[4];
+        return { table: schema ? `${schema}.${table}` : table, columns };
     }
     return false;
 }