84 lines
2.6 KiB
JavaScript
84 lines
2.6 KiB
JavaScript
/* Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved. */
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/******************************************************************************
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*
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* You may not use the identified files except in compliance with the Apache
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* License, Version 2.0 (the "License.")
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*
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* You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0.
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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*
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* NAME
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* rowlimit.js
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*
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* DESCRIPTION
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* Shows ways to limit the number of records fetched by queries.
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*
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* Although maxRows can be used to control the number of rows available to the
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* application, it is more efficient for the database if the SQL query syntax
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* limits the number of rows returned from the database. Use maxRows to
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* prevent badly coded queries from over-consuming Node.js resources, or when
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* the number of rows to be selected is a known, small value.
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*
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* This example uses Node 8's async/await syntax.
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*
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*****************************************************************************/
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const oracledb = require('oracledb');
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const dbConfig = require('./dbconfig.js');
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const demoSetup = require('./demosetup.js');
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const myoffset = 1; // number of rows to skip
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const mymaxnumrows = 2; // number of rows to fetch
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async function run() {
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let connection;
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try {
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connection = await oracledb.getConnection(dbConfig);
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await demoSetup.setupBf(connection); // create the demo table
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let sql = `SELECT id, farmer FROM no_banana_farmer ORDER BY id`;
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if (connection.oracleServerVersion >= 1201000000) {
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// 12c row-limiting syntax
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sql += ` OFFSET :offset ROWS FETCH NEXT :maxnumrows ROWS ONLY`;
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} else {
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// Pre-12c syntax [you could also customize the original query and use row_number()]
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sql = `SELECT * FROM (SELECT A.*, ROWNUM AS MY_RNUM FROM ( ${sql} ) A
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WHERE ROWNUM <= :maxnumrows + :offset) WHERE MY_RNUM > :offset`;
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}
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const result = await connection.execute(
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sql,
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{ offset: myoffset, maxnumrows: mymaxnumrows }
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);
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console.log("Executed: " + sql);
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console.log("Number of rows returned: " + result.rows.length);
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console.log(result.rows);
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} catch (err) {
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console.error(err);
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} finally {
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if (connection) {
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try {
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await connection.close();
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} catch (err) {
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console.error(err);
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}
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}
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}
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}
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run();
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