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๐Ÿ“š Computer Science/CS 3

[SQLD ์ž๊ฒฉ์ฆ] ์ž๊ฒฉ ์˜๊ตฌ๊ฐฑ์‹  ๋ฐ ๋ณด์ˆ˜๊ต์œก ์ˆ˜๋ฃŒ ๋ฐฉ๋ฒ•

SQLD ์ž๊ฒฉ์ฆ์€ 1๋…„ 6๊ฐœ์›” ์ดํ›„๋ถ€ํ„ฐ 2๋…„ ์ด๋‚ด์— ๋ณด์ˆ˜๊ต์œก์„ ์ถ”๊ฐ€๋กœ ๋ฐ›์•„์•ผ ์œ ํšจ๊ธฐ๊ฐ„ 2๋…„ -> ์˜๊ตฌ๋กœ ์ž๊ฒฉ์„ ์œ ์ง€ํ•  ์ˆ˜ ์žˆ์Šต๋‹ˆ๋‹ค. ์ €๋„ 2๋…„์ด ๋‹ค๋˜์–ด๊ฐ€์„œ ๋ณด์ˆ˜๊ต์œก ๋ฐ›๊ณ  ์˜๊ตฌ ๊ฐฑ์‹ ํ–ˆ์–ด์š”. ์ž๊ฒฉ ์˜๊ตฌ๊ฐฑ์‹  ๋ฐ ๋ณด์ˆ˜๊ต์œก ์ˆ˜๋ฃŒ๋ฐฉ๋ฒ•์€ ์•„๋ž˜์™€ ๊ฐ™์Šต๋‹ˆ๋‹ค. 1. ๋ฐ์ดํ„ฐ์ž๊ฒฉ์‹œํ—˜ ์‚ฌ์ดํŠธ ๋กœ๊ทธ์ธ https://www.dataq.or.kr/ https://www.dataq.or.kr/ www.dataq.or.kr 2. ๋งˆ์ดํŽ˜์ด์ง€ > ๋ณด์ˆ˜๊ต์œก์—์„œ ํ•ด๋‹น ์ž๊ฒฉ์ฆ ๋ณด์ˆ˜๊ต์œก ์ง„ํ–‰ 3. 4์‹œ๊ฐ„์งœ๋ฆฌ ๊ฐ•์˜ ๋“ฃ๊ธฐ ์ค‘๊ฐ„์— ๋ณด๊ณ ์žˆ๋Š”์ง€ ํ™•์ธํ•˜๋Š”๊ฑฐ ์—†๊ณ  ๋„˜๊ธฐ๋Š”๊ฑฐ ์—†์–ด์„œ ๊ฑ ๋ผ๋””์˜ค์ฒ˜๋Ÿผ ํ‹€์–ด๋†“์œผ๋ฉด๋จ ํ—ฟ. 4. ๊ฐฑ์‹ ์™„~

[Diagram] ๋‹ค์ด์–ด๊ทธ๋žจ ๊ทธ๋ฆฌ๋Š” ๋ฌด๋ฃŒ ์‚ฌ์ดํŠธ ๊ณต์œ /์ถ”์ฒœ

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[Database] SQL ๋ฌธ ์ •๋ฆฌ(์ฝ”๋”ฉ ํ…Œ์ŠคํŠธ ๋Œ€๋น„)

1. SELECT(๊ฒ€์ƒ‰) 1) ํ…Œ์ด๋ธ”์˜ ํŠน์ • ์นผ๋Ÿผ์„ ๋ถˆ๋Ÿฌ์˜ฌ ๋•Œ SELECT ์นผ๋Ÿผ๋ช… FROM ํ…Œ์ด๋ธ”๋ช…; ์—ฌ๋Ÿฌ ๊ฐœ์˜ ์นผ๋Ÿผ์„ ๋ถˆ๋Ÿฌ์˜ฌ ๋•Œ๋Š” ์ฝค๋งˆ(,)๋ฅผ ์‚ฌ์šฉํ•œ๋‹ค. SELECT ์นผ๋Ÿผ๋ช…1, ์นผ๋Ÿผ๋ช…2, ์นผ๋Ÿผ๋ช…3 FROM ํ…Œ์ด๋ธ”๋ช…; ๋ชจ๋“  ์นผ๋Ÿผ์€ * ๊ธฐํ˜ธ ์‚ฌ์šฉ SELECT * FROM ํ…Œ์ด๋ธ”๋ช…; AS ๊ตฌ๋ฌธ์„ ์‚ฌ์šฉํ•˜์—ฌ ๋ณ„๋ช…(์ƒˆ๋กœ์šด ์ด๋ฆ„)์„ ๋ถ™์ผ ์ˆ˜ ์žˆ๋‹ค. SELECT ์นผ๋Ÿผ1 AS ๋ณ„๋ช…1 FROM ํ…Œ์ด๋ธ”๋ช…; ์ค‘๋ณต์„ ์ œ์™ธํ•˜๊ณ  ๊ฐ€์ ธ์˜ค๊ณ  ์‹ถ์„ ๋•Œ๋Š” DISTINCT ์—ฐ์‚ฐ์ž๋ฅผ ์“ด๋‹ค. ๋ฐ์ดํ„ฐ๋Š” ์˜ค๋ฆ„์ฐจ์ˆœ์œผ๋กœ ์ •๋ ฌ๋œ๋‹ค. SELECT DISTINCT ์นผ๋Ÿผ๋ช… FROM ํ…Œ์ด๋ธ”๋ช…; 2) ํŠน์ • ์กฐ๊ฑด์„ ๋งŒ์กฑํ•˜๋Š” ์นผ๋Ÿผ์„ ๋ถˆ๋Ÿฌ์˜ฌ ๋•Œ SELECT ์นผ๋Ÿผ๋ช… FROM ํ…Œ์ด๋ธ”๋ช… WHERE ์นผ๋Ÿผ๋ช… = ๊ฐ’; /*์กฐ๊ฑด๋น„๊ต๋Š” =, !=, , =, IS NULL ๋“ฑ์ด ..

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