108 lines
3.8 KiB
JavaScript
108 lines
3.8 KiB
JavaScript
/* Copyright (c) 2015, 2022, Oracle and/or its affiliates. */
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/******************************************************************************
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*
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* This software is dual-licensed to you under the Universal Permissive License
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* (UPL) 1.0 as shown at https://oss.oracle.com/licenses/upl and Apache License
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* 2.0 as shown at http://www.apache.org/licenses/LICENSE-2.0. You may choose
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* either license.
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*
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* If you elect to accept the software under the Apache License, Version 2.0,
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* the following applies:
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://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,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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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 fs = require('fs');
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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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// On Windows and macOS, you can specify the directory containing the Oracle
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// Client Libraries at runtime, or before Node.js starts. On other platforms
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// the system library search path must always be set before Node.js is started.
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// See the node-oracledb installation documentation.
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// If the search path is not correct, you will get a DPI-1047 error.
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let libPath;
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if (process.platform === 'win32') { // Windows
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libPath = 'C:\\oracle\\instantclient_19_12';
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} else if (process.platform === 'darwin') { // macOS
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libPath = process.env.HOME + '/Downloads/instantclient_19_8';
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}
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if (libPath && fs.existsSync(libPath)) {
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oracledb.initOracleClient({ libDir: libPath });
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}
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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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{ prefetchRows: mymaxnumrows + 1, fetchArraySize: 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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