Export methods to get max, min, values od a column and sample based on a range

lib/cartodb/utils/query-utils.js

@@ -150,6 +150,36 @@ function simpleQueryTable(sql) {
     return false;
 }
 
+module.exports.getMaxMinColumnQuery = function (query, column = 'cartodb_id') {
+    return `
+        SELECT
+            min(${column}) AS min_id,
+            max(${column}) AS max_id,
+            (max(${column}) - min(${column})) AS id_span
+        FROM (${query}) _cdb_metadata_max_min;
+    `;
+};
+
+module.exports.getSampleValuesFromRange = function getSampleValuesFromRange (min, span, limit) {
+    const sample = new Set();
+
+    limit = limit < span ? limit : span;
+
+    while (sample.size < limit) {
+        sample.add(Math.floor(min + Math.random() * span));
+    }
+
+    return Array.from(sample);
+};
+
+module.exports.getSampleFromIdsQuery = function (query, ids, columns, column = 'cartodb_id') {
+    return `
+        SELECT
+            ${columnSelector(columns)}
+        FROM (${query}) _cdb_metadata_sample
+        WHERE ${column} IN (${ids.join(',')})
+    `;
+};
 
 function getQueryLimited(query, limit = 0) {
     return `