create knex migration code example

Example 1: move records from table to another using knex migration

// modified by Emmanuel Mahuni to use async/await more readable code
exports.up = async function(knex) {
 	await knex.schema.createTable('table_b', t => {
      t.string('col_a')
      t.string('col_b')
    })
  
    await knex.schema.createTable('table_c', t => {
      t.string('col_c')
      t.string('col_d')
    })
  
    let rows = await knex('table_a').select('col_a', 'col_b')
    await knex('table_b').insert(rows)
    
  	rows = await knex('table_a').select('col_c', 'col_d')
    await knex('table_c').insert(rows)
  
    await knex.schema.dropTableIfExists('table_a'))
};

exports.down = async function(knex) {
  await knex.schema.createTable('table_a', t => {
      t.string('col_a')
      t.string('col_b')
      t.string('col_c')
      t.string('col_d')
    })
  
  let rows = await knex('table_b').select('col_a', 'col_b')
  await knex('table_a').insert(rows)
  
  rows = await knex('table_c').select('col_c', 'col_d')
  await knex('table_a').insert(rows)
  
  await knex.schema.dropTableIfExists('table_b')
  await knex.schema.dropTableIfExists('table_c')
};

Example 2: knex migration

// best tutorial knex migration
https://www.youtube.com/watch?v=ipAH7lMfq7k
https://www.youtube.com/watch?v=U7GjS3FuSkA