A SQL database engine written in JavaScript diff --git a/src/csvReader.js b/src/csvReader.js index e69de29bb..b1d92429a 100644 --- a/src/csvReader.js +++ b/src/csvReader.js @@ -0,0 +1,20 @@ +const fs = require('fs'); +const csv = require('csv-parser'); + +function readCSV(filePath) { + const results = []; + + return new Promise((resolve, reject) => { + fs.createReadStream(filePath) + .pipe(csv()) + .on('data', (data) => results.push(data)) + .on('end', () => { + resolve(results); + }) + .on('error', (error) => { + reject(error); + }); + }); +} + +module.exports = readCSV; diff --git a/src/index.js b/src/index.js new file mode 100644 index 000000000..bbdf47bac --- /dev/null +++ b/src/index.js @@ -0,0 +1,276 @@ +const { parseQuery } = require('./queryParser'); +const readCSV = require('./csvReader'); +function performInnerJoin(data, joinData, joinCondition, fields, table) { + return data.flatMap(mainRow => { + return joinData + .filter(joinRow => { + const mainValue = mainRow[joinCondition.left.split('.')[1]]; + const joinValue = joinRow[joinCondition.right.split('.')[1]]; + return mainValue === joinValue; + }) + .map(joinRow => { + return fields.reduce((acc, field) => { + const [tableName, fieldName] = field.split('.'); + acc[field] = tableName === table ? mainRow[fieldName] : joinRow[fieldName]; + return acc; + }, {}); + }); + }); +} +function performLeftJoin(data, joinData, joinCondition, fields, table) { + return data.flatMap(mainRow => { + const matchingJoinRows = joinData.filter(joinRow => { + const mainValue = getValueFromRow(mainRow, joinCondition.left); + const joinValue = getValueFromRow(joinRow, joinCondition.right); + return mainValue === joinValue; + }); + if (matchingJoinRows.length === 0) { + return [createResultRow(mainRow, null, fields, table, true)]; + } + return matchingJoinRows.map(joinRow => createResultRow(mainRow, joinRow, fields, table, true)); + }); +} +function getValueFromRow(row, compoundFieldName) { + const [tableName, fieldName] = compoundFieldName.split('.'); + return row[`${tableName}.${fieldName}`] || row[fieldName]; +} +function performRightJoin(data, joinData, joinCondition, fields, table) { + // Cache the structure of a main table row (keys only) + const mainTableRowStructure = data.length > 0 ? Object.keys(data[0]).reduce((acc, key) => { + acc[key] = null; // Set all values to null initially + return acc; + }, {}) : {}; + return joinData.map(joinRow => { + const mainRowMatch = data.find(mainRow => { + const mainValue = getValueFromRow(mainRow, joinCondition.left); + const joinValue = getValueFromRow(joinRow, joinCondition.right); + return mainValue === joinValue; + }); + // Use the cached structure if no match is found + const mainRowToUse = mainRowMatch || mainTableRowStructure; + // Include all necessary fields from the 'student' table + return createResultRow(mainRowToUse, joinRow, fields, table, true); + }); +} +function createResultRow(mainRow, joinRow, fields, table, includeAllMainFields) { + const resultRow = {}; + if (includeAllMainFields) { + // Include all fields from the main table + Object.keys(mainRow || {}).forEach(key => { + const prefixedKey = `${table}.${key}`; + resultRow[prefixedKey] = mainRow ? mainRow[key] : null; + }); + } + // Now, add or overwrite with the fields specified in the query + fields.forEach(field => { + const [tableName, fieldName] = field.includes('.') ? field.split('.') : [table, field]; + resultRow[field] = tableName === table && mainRow ? mainRow[fieldName] : joinRow ? joinRow[fieldName] : null; + }); + return resultRow; +} +function evaluateCondition(row, clause) { + let { field, operator, value } = clause; + // Check if the field exists in the row + if (row[field] === undefined) { + throw new Error(`Invalid field: ${field}`); + } + // Parse row value and condition value based on their actual types + const rowValue = parseValue(row[field]); + let conditionValue = parseValue(value); + switch (operator) { + case '=': return rowValue === conditionValue; + case '!=': return rowValue !== conditionValue; + case '>': return rowValue > conditionValue; + case '<': return rowValue < conditionValue; + case '>=': return rowValue >= conditionValue; + case '<=': return rowValue <= conditionValue; + default: throw new Error(`Unsupported operator: ${operator}`); + } +} +// Helper function to parse value based on its apparent type +function parseValue(value) { + // Return null or undefined as is + if (value === null || value === undefined) { + return value; + } + // If the value is a string enclosed in single or double quotes, remove them + if (typeof value === 'string' && ((value.startsWith("'") && value.endsWith("'")) || (value.startsWith('"') && value.endsWith('"')))) { + value = value.substring(1, value.length - 1); + } + // Check if value is a number + if (!isNaN(value) && value.trim() !== '') { + return Number(value); + } + // Assume value is a string if not a number + return value; +} +function applyGroupBy(data, groupByFields, aggregateFunctions) { + const groupResults = {}; + data.forEach(row => { + // Generate a key for the group + const groupKey = groupByFields.map(field => row[field]).join('-'); + // Initialize group in results if it doesn't exist + if (!groupResults[groupKey]) { + groupResults[groupKey] = { count: 0, sums: {}, mins: {}, maxes: {} }; + groupByFields.forEach(field => groupResults[groupKey][field] = row[field]); + } + // Aggregate calculations + groupResults[groupKey].count += 1; + aggregateFunctions.forEach(func => { + const match = /(\w+)\((\w+)\)/.exec(func); + if (match) { + const [, aggFunc, aggField] = match; + const value = parseFloat(row[aggField]); + switch (aggFunc.toUpperCase()) { + case 'SUM': + groupResults[groupKey].sums[aggField] = (groupResults[groupKey].sums[aggField] || 0) + value; + break; + case 'MIN': + groupResults[groupKey].mins[aggField] = Math.min(groupResults[groupKey].mins[aggField] || value, value); + break; + case 'MAX': + groupResults[groupKey].maxes[aggField] = Math.max(groupResults[groupKey].maxes[aggField] || value, value); + break; + // Additional aggregate functions can be added here + } + } + }); + }); + // Convert grouped results into an array format + return Object.values(groupResults).map(group => { + // Construct the final grouped object based on required fields + const finalGroup = {}; + groupByFields.forEach(field => finalGroup[field] = group[field]); + aggregateFunctions.forEach(func => { + const match = /(\w+)\((\*|\w+)\)/.exec(func); + if (match) { + const [, aggFunc, aggField] = match; + switch (aggFunc.toUpperCase()) { + case 'SUM': + finalGroup[func] = group.sums[aggField]; + break; + case 'MIN': + finalGroup[func] = group.mins[aggField]; + break; + case 'MAX': + finalGroup[func] = group.maxes[aggField]; + break; + case 'COUNT': + finalGroup[func] = group.count; + break; + // Additional aggregate functions can be handled here + } + } + }); + return finalGroup; + }); +} + +async function executeSELECTQuery(query) { + try { + + const { fields, table, whereClauses, joinType, joinTable, joinCondition, groupByFields, hasAggregateWithoutGroupBy, orderByFields, limit } = parseQuery(query); + let data = await readCSV(`${table}.csv`); + + // Perform INNER JOIN if specified + if (joinTable && joinCondition) { + const joinData = await readCSV(`${joinTable}.csv`); + switch (joinType.toUpperCase()) { + case 'INNER': + data = performInnerJoin(data, joinData, joinCondition, fields, table); + break; + case 'LEFT': + data = performLeftJoin(data, joinData, joinCondition, fields, table); + break; + case 'RIGHT': + data = performRightJoin(data, joinData, joinCondition, fields, table); + break; + default: + throw new Error(`Unsupported JOIN type: ${joinType}`); + } + } + // Apply WHERE clause filtering after JOIN (or on the original data if no join) + let filteredData = whereClauses.length > 0 + ? data.filter(row => whereClauses.every(clause => evaluateCondition(row, clause))) + : data; + +let groupResults = filteredData; +if (hasAggregateWithoutGroupBy) { + // Special handling for queries like 'SELECT COUNT(*) FROM table' + const result = {}; + + fields.forEach(field => { + const match = /(\w+)\((\*|\w+)\)/.exec(field); + if (match) { + const [, aggFunc, aggField] = match; + switch (aggFunc.toUpperCase()) { + case 'COUNT': + result[field] = filteredData.length; + break; + case 'SUM': + result[field] = filteredData.reduce((acc, row) => acc + parseFloat(row[aggField]), 0); + break; + case 'AVG': + result[field] = filteredData.reduce((acc, row) => acc + parseFloat(row[aggField]), 0) / filteredData.length; + break; + case 'MIN': + result[field] = Math.min(...filteredData.map(row => parseFloat(row[aggField]))); + break; + case 'MAX': + result[field] = Math.max(...filteredData.map(row => parseFloat(row[aggField]))); + break; + } + } + }); + return [result]; + // Add more cases here if needed for other aggregates +} else if (groupByFields) { + groupResults = applyGroupBy(filteredData, groupByFields, fields); + + // order + let orderedResults = groupResults; + if (orderByFields) { + orderedResults = groupResults.sort((a, b) => { + for (let { fieldName, order } of orderByFields) { + if (a[fieldName] < b[fieldName]) return order === 'ASC' ? -1 : 1; + if (a[fieldName] > b[fieldName]) return order === 'ASC' ? 1 : -1; + } + return 0; + }); + } + if (limit !== null) { + groupResults = groupResults.slice(0, limit); + } + return groupResults; +} else { + + let orderedResults = groupResults; + if (orderByFields) { + orderedResults = groupResults.sort((a, b) => { + for (let { fieldName, order } of orderByFields) { + if (a[fieldName] < b[fieldName]) return order === 'ASC' ? -1 : 1; + if (a[fieldName] > b[fieldName]) return order === 'ASC' ? 1 : -1; + } + return 0; + }); + } + + if (limit !== null) { + orderedResults = orderedResults.slice(0, limit); + } + + // Select the specified fields + return orderedResults.map(row => { + const selectedRow = {}; + fields.forEach(field => { + // Assuming 'field' is just the column name without table prefix + selectedRow[field] = row[field]; + }); + return selectedRow; + }); +} +} catch (error) { + throw new Error(`Error executing query: ${error.message}`); +} +} +module.exports=executeSELECTQuery; \ No newline at end of file diff --git a/src/queryParser.js b/src/queryParser.js new file mode 100644 index 000000000..f48cb412c --- /dev/null +++ b/src/queryParser.js @@ -0,0 +1,116 @@ +// /*****STEP : 13**************** */ +function parseQuery(query) { + // Trim the query to remove any leading/trailing whitespaces + try{ + query = query.trim(); + + //Updated regex to capture LIMIT clause and remove it for further processing + const limitRegex = /\sLIMIT\s(\d+)/i; + const limitMatch = query.match(limitRegex); + + let limit = null; + if (limitMatch) { + limit = parseInt(limitMatch[1], 10); + query = query.replace(limitRegex, ''); // Remove LIMIT clause + } + + // Process ORDER BY clause and remove it for further processing + const orderByRegex = /\sORDER BY\s(.+)/i; + const orderByMatch = query.match(orderByRegex); + + let orderByFields = null; + if (orderByMatch) { + orderByFields = orderByMatch[1].split(',').map(field => { + const [fieldName, order] = field.trim().split(/\s+/); + return { fieldName, order: order ? order.toUpperCase() : 'ASC' }; + }); + query = query.replace(orderByRegex, ''); + } + // Process GROUP BY clause and remove it for further processing + const groupByRegex = /\sGROUP BY\s(.+)/i; + const groupByMatch = query.match(groupByRegex); + + let groupByFields = null; + if (groupByMatch) { + groupByFields = groupByMatch[1].split(',').map(field => field.trim()); + query = query.replace(groupByRegex, ''); + } + + const whereSplit = query.split(/\sWHERE\s/i); + const queryWithoutWhere = whereSplit[0]; // Everything before WHERE clause + const whereClause = whereSplit.length > 1 ? whereSplit[1].trim() : null; + + const joinSplit = queryWithoutWhere.split(/\s(INNER|LEFT|RIGHT) JOIN\s/i); + const selectPart = joinSplit[0].trim(); // Everything before JOIN clause + + // Extract JOIN information + const { joinType, joinTable, joinCondition } = parseJoinClause(queryWithoutWhere); + + // Parse SELECT part + const selectRegex = /^SELECT\s(.+?)\sFROM\s(.+)/i; + const selectMatch = selectPart.match(selectRegex); + if (!selectMatch) { + throw new Error("Invalid SELECT format"); + } + const [, fields, table] = selectMatch; + // Parse WHERE part if it exists + let whereClauses = []; + if (whereClause) { + whereClauses = parseWhereClause(whereClause); + } + // Check for aggregate functions without GROUP BY + const hasAggregateWithoutGroupBy = checkAggregateWithoutGroupBy(query, groupByFields); + + return { + fields: fields.split(',').map(field => field.trim()), + table: table.trim(), + whereClauses, + joinType, + joinTable, + joinCondition, + groupByFields, + orderByFields, + hasAggregateWithoutGroupBy, + limit + }; + }catch(err){ + throw new Error(`Query parsing error: ${err.message}`); + } +} + +function checkAggregateWithoutGroupBy(query, groupByFields) { + const aggregateFunctionRegex = /(\bCOUNT\b|\bAVG\b|\bSUM\b|\bMIN\b|\bMAX\b)\s*\(\s*(\*|\w+)\s*\)/i; + return aggregateFunctionRegex.test(query) && !groupByFields; +} + +function parseWhereClause(whereString) { + const conditionRegex = /(.*?)(=|!=|>|<|>=|<=)(.*)/; + return whereString.split(/ AND | OR /i).map(conditionString => { + const match = conditionString.match(conditionRegex); + if (match) { + const [, field, operator, value] = match; + return { field: field.trim(), operator, value: value.trim() }; + } + throw new Error('Invalid WHERE clause format'); + }); +} +function parseJoinClause(query) { + const joinRegex = /\s(INNER|LEFT|RIGHT) JOIN\s(.+?)\sON\s([\w.]+)\s*=\s*([\w.]+)/i; + const joinMatch = query.match(joinRegex); + if (joinMatch) { + return { + joinType: joinMatch[1].trim(), + joinTable: joinMatch[2].trim(), + joinCondition: { + left: joinMatch[3].trim(), + right: joinMatch[4].trim() + } + }; + } + return { + joinType: null, + joinTable: null, + joinCondition: null + }; +} +module.exports = { parseQuery, parseJoinClause };