Почему поиск без индекса быстрее поиска с индексом?

@Table({tableName: ‘chats’, createdAt: false, updatedAt: false})
export class MessageTable extends Model {

@Column({type: DataType.INTEGER, primaryKey: true, unique: true, autoIncrement: true})
id: number;

@Column({type: DataType.JSON})
members: number[];

@Index(‘key’)
@Column({type: DataType.TEXT})
chatKey: string;

@Column({type: DataType.INTEGER})
author: number;

@Column({type: DataType.STRING(32)})
date: string;

@Column({type: DataType.STRING(255)})
data: string;

@Column({type: DataType.STRING(511)})
files: string;

}

addMessage = (number: number) => {
return new Promise( (res) => {
this.ChatRepository.create({
id: 20000000 + number,
author: number,
date: ‘asd’,
chatKey: (20000000 + number).toString(),
data: ‘das’,
files: ‘[]’,
members: [1]
}).then( () => {return res(‘das’)});
})
}

getMessageByKey = (number) => {
return new Promise( (res) => {
this.ChatRepository.findAll({where: {chatKey: number.toString()} } )
.then( (response) => res(response))
})
}

getMessagesByKey = (number) => {
return new Promise( (res) => {
this.ChatRepository.findAll({where: {
chatKey: {
[Op.like]: `%${number.toString()}%`
}
} } )
.then( (response) => res(response))
})
}
for (let indexx = 0; indexx < 100; indexx++) {
this.messageService.addMessage(indexx + 3)
.then( () => {if (indexx === 99) {
console.log(‘Ready by ‘ + (Date.now() — this.DateNow) );
} })
}
this.messageService.getMessageByKey(100000).then( (res) => {
console.log(res);
console.log(‘Ready by ‘ + (Date.now() — this.DateNow));
})

this.messageService.getMessageByKey(20000000).then( (res) => {
console.log(res);
console.log(‘Ready by ‘ + (Date.now() — this.DateNow));
})

this.messageService.getMessagesByKey(2555).then( () => {
console.log(‘Ready by ‘ + (Date.now() — this.DateNow));
})